diff --git a/docs/ptoas-tile-fusion-design.md b/docs/ptoas-tile-fusion-design.md
index 88da712ca..2eefbc3ce 100644
--- a/docs/ptoas-tile-fusion-design.md
+++ b/docs/ptoas-tile-fusion-design.md
@@ -203,7 +203,7 @@ PTO 指令在 Davinci 架构上以 Unified Buffer（UB）中驻留的数据块
 
 - `--pto-backend=vpto`
 - `--pto-arch=a5`
-- 显式传入 `--enable-op-fusion`
+- `--enable-op-fusion` 未显式设置时默认开启；可通过 `--enable-op-fusion=false` 关闭
 
 #### 4.2.2 输入层级支持
 
@@ -255,7 +255,7 @@ PTO 指令在 Davinci 架构上以 Unified Buffer（UB）中驻留的数据块
 #### 4.2.4 非目标路径
 
 - EmitC 后端会忽略 `--enable-op-fusion`。
-- 未开启 `--enable-op-fusion` 时，普通 VPTO 路径不会形成 `pto.fusion_region`，也不会进入 post-lowering 融合生命周期。
+- 显式传入 `--enable-op-fusion=false` 时，普通 VPTO 路径不会形成 `pto.fusion_region`，也不会进入 post-lowering 融合生命周期。
 - 后端分界线已固定为 `ExpandTileOp`；原有的 `View2Memref` / `PTOToA5VM` 主线已移除。
 
 ---
diff --git a/test/lit/tile_fusion/op_fusion_cli_flags.pto b/test/lit/tile_fusion/op_fusion_cli_flags.pto
index 0c9ee9960..fabc5e443 100644
--- a/test/lit/tile_fusion/op_fusion_cli_flags.pto
+++ b/test/lit/tile_fusion/op_fusion_cli_flags.pto
@@ -6,13 +6,14 @@
 // INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.
 // See LICENSE in the root of the software repository for the full text of the License.
 
-// Guards --enable-op-fusion CLI visibility and warning behavior on the
+// Guards --enable-op-fusion CLI visibility and tri-state behavior on the
 // EmitC mainline frontend-fusion gate.
 //
 // RUN: ptoas --help-hidden 2>&1 | FileCheck %s --check-prefix=HELP
-// RUN: ptoas --pto-arch=a5 --pto-level=level2 --enable-op-fusion %s -o /dev/null 2>&1 | FileCheck %s --allow-empty --check-prefix=LEVEL2
-// RUN: ptoas --pto-arch=a5 --pto-level=level1 --enable-op-fusion %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=LEVEL1
-// RUN: ptoas --pto-arch=a3 --enable-op-fusion %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=A3
+// RUN: ptoas --pto-arch=a5 --pto-level=level2 %s -o /dev/null 2>&1 | FileCheck %s --allow-empty --check-prefix=DEFAULT-A5
+// RUN: ptoas --pto-arch=a5 --pto-level=level2 --enable-op-fusion=false %s -o /dev/null 2>&1 | FileCheck %s --allow-empty --check-prefix=DISABLE-A5
+// RUN: ptoas --pto-arch=a5 --pto-level=level1 --enable-op-fusion=true %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=LEVEL1
+// RUN: not ptoas --pto-arch=a3 --enable-op-fusion=true %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=A3
 
 module {
   func.func @fusion_cli_flags() {
@@ -22,8 +23,12 @@ module {
 
 // HELP: --enable-op-fusion
 
-// LEVEL2-NOT: Warning: --enable-op-fusion is ignored
+// DEFAULT-A5-NOT: Warning:
+// DEFAULT-A5-NOT: Error:
 
-// LEVEL1: Warning: --enable-op-fusion is ignored because --pto-level=level2 or level3 is required.
+// DISABLE-A5-NOT: Warning:
+// DISABLE-A5-NOT: Error:
 
-// A3: Warning: --enable-op-fusion is ignored because --pto-arch=a5 is required.
+// LEVEL1: Warning: --enable-op-fusion=true is ignored because --pto-level=level2 or level3 is required.
+
+// A3: Error: --enable-op-fusion=true requires --pto-arch=a5.
diff --git a/test/lit/tile_fusion/op_fusion_nonfused_control.pto b/test/lit/tile_fusion/op_fusion_nonfused_control.pto
index dc753b288..7bedae91b 100644
--- a/test/lit/tile_fusion/op_fusion_nonfused_control.pto
+++ b/test/lit/tile_fusion/op_fusion_nonfused_control.pto
@@ -7,13 +7,15 @@
 // See LICENSE in the root of the software repository for the full text of the License.
 
 // Guards the non-fused control surface for frontend fusion:
-// - no flag keeps the baseline unfused
-// - A3 with the flag warns and stays unfused
-// - level1 with the flag warns and stays unfused
+// - A5 level2 defaults to fused unless explicitly disabled
+// - A5 level2 with --enable-op-fusion=false stays unfused
+// - A3 with --enable-op-fusion=true is rejected
+// - level1 with --enable-op-fusion=true warns and stays unfused
 //
-// RUN: ptoas --pto-arch=a5 --pto-level=level2 --emit-pto-ir %s -o - | FileCheck %s --check-prefix=NOFUSE
-// RUN: ptoas --pto-arch=a3 --enable-op-fusion --emit-pto-ir %s -o - 2>&1 | FileCheck %s --check-prefix=A3
-// RUN: ptoas --pto-arch=a5 --pto-level=level1 --enable-op-fusion --emit-pto-ir %s -o - 2>&1 | FileCheck %s --check-prefix=LEVEL1
+// RUN: ptoas --pto-arch=a5 --pto-level=level2 --emit-pto-ir %s -o - | FileCheck %s --check-prefix=DEFAULTA5
+// RUN: ptoas --pto-arch=a5 --pto-level=level2 --enable-op-fusion=false --emit-pto-ir %s -o - | FileCheck %s --check-prefix=NOFUSE
+// RUN: not ptoas --pto-arch=a3 --enable-op-fusion=true --emit-pto-ir %s -o - 2>&1 | FileCheck %s --check-prefix=A3
+// RUN: ptoas --pto-arch=a5 --pto-level=level1 --enable-op-fusion=true --emit-pto-ir %s -o - 2>&1 | FileCheck %s --check-prefix=LEVEL1
 
 module {
   func.func @fusion_nonfused_control(
@@ -36,13 +38,11 @@ module {
 // NOFUSE-NEXT: pto.tadd ins(
 // NOFUSE: return
 
-// A3: Warning: --enable-op-fusion is ignored because --pto-arch=a5 is required.
-// A3-LABEL: func.func @fusion_nonfused_control(
-// A3-NOT: pto.fusion_region
-// A3: pto.tadd ins(
-// A3-NEXT: pto.tadd ins(
+// DEFAULTA5-LABEL: func.func @fusion_nonfused_control(
+// DEFAULTA5: pto.fusion_region
 
-// LEVEL1: Warning: --enable-op-fusion is ignored because --pto-level=level2 or level3 is required.
+// A3: Error: --enable-op-fusion=true requires --pto-arch=a5.
+// LEVEL1: Warning: --enable-op-fusion=true is ignored because --pto-level=level2 or level3 is required.
 // LEVEL1-LABEL: func.func @fusion_nonfused_control(
 // LEVEL1-NOT: pto.fusion_region
 // LEVEL1: pto.tadd ins(
diff --git a/tools/ptoas/ptoas.cpp b/tools/ptoas/ptoas.cpp
index 5bb682167..9f9a89fff 100644
--- a/tools/ptoas/ptoas.cpp
+++ b/tools/ptoas/ptoas.cpp
@@ -422,11 +422,12 @@ static pto::ExpandTileOpOptions resolveExpandTileOpOptions(int argc,
   return expandOpts;
 }
 
-static llvm::cl::opt<bool> enableOpFusion(
+static llvm::cl::opt<llvm::cl::boolOrDefault> enableOpFusion(
     "enable-op-fusion",
-    llvm::cl::desc("Enable A5 tile fusion on level2/level3. EmitC uses "
-                   "last-use annotation; VPTO uses fusion-region lifecycle."),
-    llvm::cl::init(false));
+    llvm::cl::desc("Control A5 tile fusion on level2/level3. Defaults to "
+                   "enabled on A5, disabled on A3. EmitC uses last-use "
+                   "annotation; VPTO uses fusion-region lifecycle."),
+    llvm::cl::init(llvm::cl::BOU_UNSET));
 
 static llvm::cl::opt<bool> disableInferLayout(
     "disable-infer-layout",
@@ -1612,18 +1613,25 @@ int mlir::pto::compilePTOASModule(
     return 1;
   }
 
-  if (enableOpFusion) {
-    if (arch != "a5") {
-      llvm::errs() << "Warning: --enable-op-fusion is ignored because "
-                      "--pto-arch=a5 is required.\n";
-    } else if (effectiveLevel == PTOBuildLevel::Level1) {
-      llvm::errs() << "Warning: --enable-op-fusion is ignored because "
-                      "--pto-level=level2 or level3 is required.\n";
-    }
+  const bool requestedEnableOpFusion = enableOpFusion == llvm::cl::BOU_TRUE;
+  const bool explicitDisableOpFusion = enableOpFusion == llvm::cl::BOU_FALSE;
+  const bool defaultEnableOpFusion =
+      enableOpFusion == llvm::cl::BOU_UNSET && arch == "a5";
+  const bool opFusionEnabled =
+      (requestedEnableOpFusion || defaultEnableOpFusion) &&
+      !explicitDisableOpFusion;
+
+  if (requestedEnableOpFusion && arch != "a5") {
+    llvm::errs() << "Error: --enable-op-fusion=true requires --pto-arch=a5.\n";
+    return 1;
+  }
+  if (requestedEnableOpFusion && effectiveLevel == PTOBuildLevel::Level1) {
+    llvm::errs() << "Warning: --enable-op-fusion=true is ignored because "
+                    "--pto-level=level2 or level3 is required.\n";
   }
 
   const bool enableA5FusionPath =
-      enableOpFusion && arch == "a5" &&
+      opFusionEnabled && arch == "a5" &&
       effectiveLevel != PTOBuildLevel::Level1;
   const bool enableA5EmitCFusionPath =
       enableA5FusionPath && effectiveBackend == PTOBackend::EmitC;