The paper studied on a 125cc single-cylinder gasoline engine. Within the range of engine economical rotational speed, optimized structure of intake pipe can arouse airflow of inertial and resonant effect. The theoretical model analysis and computer simulation provides directional guidance of improving intake system, which may reduce test cost and shorten the redesign cycle. Through the experiment of speed characteristic on dynamometer bench, test data of original and improved intake pipes were compared. Both theoretical models and experimental results show that the effective use of intake pulsation can improve the engine power performance and fuel economy.