Abstract: To design a better rubber buffer, MSC. Marc software is adopted to analyze size effect on mechanical behavior of the rubber buffer. The results reveal that if the width or angle of slanting rib is increased, the rubber buffer can bear heavier load and reduce less vibration. But while angle of rubber buffer increases, the increase of maximal react force is not linear to the increase of rubber buffer's angle. As angle of rubber buffer increased, the maximal react force increases, that is, the ability to bear load increases dramatically.