The investment volatility is the main reason that causes business cycle and it also causes economic growth loss. The optimal investment path should be smooth in time zone. The empirical evidences show that China's fixed investment growth and investment ratio to real GDP have different relationships with economic growth.Because of the low output infrastructure investment take most part in the fixed investments the investment ratio forces economic growth weakly.The active fiscal policy should pay adequate attention to the improvements of investment terms and structures so as to help keep a sustained rapid economic growth.