diff --git a/main.cpp b/main.cpp
index c071c29..e442544 100644
--- a/main.cpp
+++ b/main.cpp
@@ -83,6 +83,7 @@ void execute(const std::string& file,const uint32_t cmd)
         parse.print();
     
     // code generator gets parser's ast and linker's import file list to generate code
+    optimize(parse.ast());
     gen.compile(parse,linker);
     if(cmd&VM_CODEINFO)
         gen.print();
diff --git a/makefile b/makefile
index beeff76..a98f9b6 100644
--- a/makefile
+++ b/makefile
@@ -1,5 +1,5 @@
 .PHONY=test
-nasal:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
+nasal:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
 	clang++ -std=c++11 -O3 main.cpp -o nasal -fno-exceptions -ldl -Wshadow -Wall
 test:nasal
 	./nasal test/ascii-art.nas
diff --git a/nasal.h b/nasal.h
index 5451c88..b9505c8 100644
--- a/nasal.h
+++ b/nasal.h
@@ -132,6 +132,7 @@ std::string rawstr(const std::string& str)
 #include "nasal_ast.h"
 #include "nasal_parse.h"
 #include "nasal_import.h"
+#include "nasal_opt.h"
 #include "nasal_gc.h"
 #include "nasal_builtin.h"
 #include "nasal_codegen.h"
diff --git a/nasal_opt.h b/nasal_opt.h
new file mode 100644
index 0000000..037c3fe
--- /dev/null
+++ b/nasal_opt.h
@@ -0,0 +1,43 @@
+#ifndef __NASAL_OPT_H__
+#define __NASAL_OPT_H__
+
+void calc_const_num(nasal_ast& root)
+{
+    auto& vec=root.child();
+    for(auto& i:vec)
+        calc_const_num(i);
+    if(root.type()!=ast_add &&
+        root.type()!=ast_sub &&
+        root.type()!=ast_mult &&
+        root.type()!=ast_div &&
+        root.type()!=ast_less &&
+        root.type()!=ast_leq &&
+        root.type()!=ast_grt &&
+        root.type()!=ast_geq)
+        return;
+    if(vec.size()!=2 || vec[0].type()!=ast_num || vec[1].type()!=ast_num)
+        return;
+    double res;
+    switch(root.type())
+    {
+        case ast_add:res=vec[0].num()+vec[1].num();break;
+        case ast_sub:res=vec[0].num()-vec[1].num();break;
+        case ast_mult:res=vec[0].num()*vec[1].num();break;
+        case ast_div:res=vec[0].num()/vec[1].num();break;
+        case ast_less:res=vec[0].num()<vec[1].num();break;
+        case ast_leq:res=vec[0].num()<=vec[1].num();break;
+        case ast_grt:res=vec[0].num()>vec[1].num();break;
+        case ast_geq:res=vec[0].num()>=vec[1].num();break;
+    }
+    if(std::isinf(res) || std::isnan(res)) // inf and nan will cause number hashmap error in codegen
+        return;
+    root.set_num(res);
+    root.child().clear();
+    root.set_type(ast_num);
+}
+void optimize(nasal_ast& root)
+{
+    for(auto& i:root.child())
+        calc_const_num(i);
+}
+#endif
\ No newline at end of file
diff --git a/test/calc.nas b/test/calc.nas
index 2125cb5..f4b9b1a 100644
--- a/test/calc.nas
+++ b/test/calc.nas
@@ -5,6 +5,7 @@ var filename=[
     "nasal_ast.h",
     "nasal_builtin.h",
     "nasal_codegen.h",
+    "nasal_opt.h",
     "nasal_gc.h",
     "nasal_import.h",
     "nasal_lexer.h",
@@ -19,6 +20,7 @@ var space=[
     "    ",
     "",
     "",
+    "    ",
     "     ",
     " ",
     "  ",