In order to avoid the interruption of power and reduce the impact of shift in a power shift tractor, the shift quality of a heavy-duty tractor power shift transmission was studied with a tractor full power shift transmission developed independently. The characteristics of torque transfer in the dynamic coupling process of the shifting clutch were analyzed. The key to the steady control of the shifting clutch was the accurate control of the clutch engagement pressure. The influence of different pressure control strategies on gear shifting quality was studied based on the overlap time of gear shifting and engagement pressure. Taking shift hydraulic impact, sliding friction and output torque as the optimization objectives, the influence of overlapping time, engagement pressure and sliding difference of the master and slave moving plate of the shift clutch on shift quality was studied. The higher the engagement pressure was, the smaller the sliding difference of the shift clutch was. If the overlap time of gear shift was too short, it would result in the decrease or interruption of tractor power. If the shift overlap time was too long, two shift clutches would be engaged for a long time at the same time and “double locking” phenomenon occurred. When the clutch was separated, there was a mutating dynamic load on the output shaft. Therefore, the shift overlap time should be controlled reasonably to achieve the best shift quality. The shift control strategy of different shift overlap time was studied. The shift quality was analyzed synthetically by combining shift hydraulic impact and sliding friction, and the optimal shift point was determined under certain conditions. The simulation results showed that when the shift overlap time was 0.3s, the shift had the lowest hydraulic impact, the least sliding friction power and the least torque loss. Besides, the shift quality was the best. The output torque of the joint pressure was the same within the range of 0.40~0.63MPa (the slip was 455.2~560.0r/min). When the joint pressure was 0.40MPa, the value of sliding friction and shifting hydraulic impact force reached the minimum. This study laid a foundation for further realization of pressure tracking and accurate control of shift clutch.