Abstract: To enhances gear contacts fatigue life,reduce heat treatment production cycle and reduce scrap ratess transmission of tractor two shaft 20CrMnTi steel gear gas carbonitriding composite catalytic were processed improvement.The improvement of the sample before the test and bench test gear were analyzed.The results show that after the heat treatment temperature from 930 ℃ to 860 ℃,penetrating time from 7 h shortened to 4.5 h,improve product wear resistance,hardness of the surface,the rate of identification of 92%.The average life expectancy increased 50%,the new technology has been applied to industrial production.