The study of motorcycle's acoustic signal shows that gears noise take a great proportion on the whole acoustic of motorcycle.So how to control the noiseof gears is very helpful for reducing the whole motor's acoustic.This paper discusses the engine matching with transmission system in reason,primary transmission and gear geometry design parameter & the mend of tooth body(tooth form & tooth direction) how to influence the acoustic of motorcycle.The study shows that the gear transmission System's matching with engine in reason can notable improve the efficiency of motorcycle.In the meaning time the exactly choosing the primary transmission gear geometry design parameter and the mend of primary transmission gear's tooth body can effectively reduce the acoustic of motorcycle.This paper has engineering practice sense.