Abstract: Aiming at problems of large total mass，low fatigue strength and poor shift ride comfort of 404P tractor gearbox gear train，a multi-objective parameter optimization mathematical model of gear train was established，which took the minimum gear total mass，the highest fatigue strength and the highest shift ride comfort as optimization objectives.A multi-objective optimization method based on NSGA-II with elite strategy was proposed.Optimization design of gear train parameters was carried out based on Matlab optimization toolbox.Results showed that difference of optimization rate for gear train mass was 187.30%，difference of optimization rate for gear train fatigue strength was 85.27%，and difference of optimization rate for gear train shift ride comfort was 9.09%.Compared with traditional experience design，transmission performance of 404P type hilly tractor was further improved.