A parallel diesel-electric hybrid tractor was taken as the research object. By analyzing the topological characteristics and working characteristics of hybrid tractors, the coupling dynamic model of tractor rotary tillage unit and ploughing unit was constructed. With the goal of minimizing the equivalent fuel consumption of the whole machine, the motor power and diesel engine power were the control variables, and the state of charge（SOC）of the battery was the state variable, and the energy-saving control strategy based on Pontryagin’s minimum principle（PMP）was established. Finally, the Matlab simulation platform was used to simulate the energy-saving control strategy based on the Pontryagin’s minimum principle for the two typical working conditions of the tractor. The control strategy based on the optimal economic curve was used as a comparison strategy to verify the control effect based on the Pontryagin’s minimum principle. The analysis and comparison of the results of these two control strategies showed that: under rotary tillage conditions, the SOC value based on the optimal economic curve control strategy was decreased rapidly, while the SOC value based on the PMP control strategy was decreased slowly. Under the ploughing condition, the SOC value based on the optimal economic curve control strategy was both increased and decreased by a large margin, while the SOC value based on the PMP control strategy was only decreased. It was shown that the energy management strategy based on the Pontriagin minimum principle can reasonably control the operating state of diesel engine and motor, so that diesel engine and motor work in highefficiency areas. It effectively reduced the equivalent fuel consumption of tractors in the field. Under rotary tillage, the equivalent fuel consumption was reduced by 10.44%;under the ploughing condition, the equivalent fuel consumption was reduced by 11.20%.