Abstract: According to the demand of powertrain of cotton picker, through analysis of external characteristics of the engine and the adjustment performance of variable pumps and constant displacement motors in fluid diver system, the advantages and disadvantages of the three powerstrain schemes of the home-made cotton picker were analyzed and compared and then the best one which could obtain stepless speed variation in different speed range was determined; The determined system was applied in self-propelled 4MZ-2/3 cotton picker industrializing production.