diff --git a/tools/onnx2bnn/onnx2bnn.cpp b/tools/onnx2bnn/onnx2bnn.cpp
index 4439375..8d3e82a 100644
--- a/tools/onnx2bnn/onnx2bnn.cpp
+++ b/tools/onnx2bnn/onnx2bnn.cpp
@@ -6,33 +6,62 @@
 #include <string>
 
 #include <common/StrKeyMap.h>
+#include <common/argh.h>
 #include <glog/logging.h>
 #include "NodeAttrHelper.h"
 #include "OnnxConverter.h"
-#include <common/argh.h>
 #include "common/log_helper.h"
 
 using std::string;
 using std::vector;
 
 void usage(const std::string &filename) {
-    std::cout << "Usage: " << filename << " onnx_model output_filename" << std::endl;
+    std::cout
+        << "Usage: " << filename
+        << " onnx_model output_filename [--optimize strict|moderate|aggressive]"
+        << std::endl;
+    std::cout << "Example: " << filename
+              << " model.onnx model.dab (The optimization leval will be "
+                 "\"aggressive\")"
+              << std::endl;
+    std::cout << "Example: " << filename
+              << " model.onnx model.dab --optimize strict (The optimization "
+                 "level will be \"strict\")"
+              << std::endl;
 }
 
 int main(int argc, char **argv) {
-    argh::parser cmdl(argc, argv);
+    argh::parser cmdl;
+    cmdl.add_param("optimize");
+    cmdl.parse(argc, argv);
     google::InitGoogleLogging(cmdl[0].c_str());
     FLAGS_alsologtostderr = true;
     if (!cmdl(2)) {
         usage(cmdl[0]);
         return -1;
     }
-    bnn::OnnxConverter::Level opt_level = bnn::OnnxConverter::Level::kModerate;
-    if (cmdl["strict"]) {
-        opt_level = bnn::OnnxConverter::Level::kStrict;
+    // flags like 'onnx2bnn --strict' is not supported now
+    for (const auto flag : cmdl.flags()) {
+        std::cout << "Invalid flag: " << flag << std::endl;
+        usage(cmdl[0]);
+        return -2;
     }
-    if (cmdl["aggressive"]) {
+
+    const std::string opt_level_str =
+        cmdl("optimize").str().empty() ? "aggressive" : cmdl("optimize").str();
+
+    bnn::OnnxConverter::Level opt_level;
+    if (opt_level_str == "strict") {
+        opt_level = bnn::OnnxConverter::Level::kStrict;
+    } else if (opt_level_str == "moderate") {
+        opt_level = bnn::OnnxConverter::Level::kModerate;
+    } else if (opt_level_str == "aggressive") {
         opt_level = bnn::OnnxConverter::Level::kAggressive;
+    } else {
+        std::cout << "Invalid optimization level: " << opt_level_str
+                  << std::endl;
+        usage(cmdl[0]);
+        return -3;
     }
 
     ONNX_NAMESPACE::ModelProto model_proto;