In order to reduce the gear screaming noise of automotive transmission,by means of Masta software,the simulation on the effects of tooth form and tooth orientation modification of the main gear pair was carried out.The influences of modified parameters on the characteristics and the error of gear transmission as well as the contact stress were investigated and formulated.The results show:appropriate tip relief can reduce the interference of gear mesh effectively;barrelling relief can improve the interference between gear root and gear tip;lead crown relief can improve the unbalance load of maximum contact stress;the combination of the whole of them can reduce gear transmission error and maximum contact stress.