Abstract: According to the characteristics of series hybrid tractors, a dynamics model of the vehicles was established, and the control strategy was designed with the thermostat type control strategy or the thermostat type + brake energy recovery control strategy. To further improve the fuel economy of series hybrid tractors, the key parameters of the thermostat type control strategy were optimized by nonlinear program genetic algorithm（NLPGA）. Through the co-simulation of AVL-Cruise and Matlab/Simulink, the results show that the three strategies can effectively maintain the battery SOC within the specified range. Under the plowing + transportation conditions, the fuel consumption of the thermostat + brake energy recovery control strategy based on NLPGA is 29.25% lower than that of the thermostat type, and it is 9.35% lower than that of the thermostat + brake energy recovery control strategy. The cumulative fuel consumption is reduced by 31.50% and 1.74%, respectively.The battery SOC is increased by 8% and 6%, respectively.