Through control of the torque transfer among several groups of wet friction clutch to realize gear shift in traveling, powershift transmission of tractor has a series of advantages, such as the engine will not flameout when overloaded, good starting performance, reducing the vibration and shock of transmission system caused by suddenly load changes. The separation and joint timing of the gearshift clutch is the key factor that affects the shifting smoothness and operating comfort of the tractor. The dynamic properties analysis method of the shift process was studied. It introduced transmission’s output speed and output torque as indexes to evaluate the productivity and power of tractor, which made up for the deficiency of traditional shift quality indexes cannot evaluate the performance of the tractor. Based on the dynamic principle, the transmission system model of the power shift tractor was constructed. The dynamic characteristics of the shift process were analyzed to research the load and power flow of clutch. The control method and control strategy of powershift transmission’s shift quality were determined. Taking the output speed variation amplitude as index to optimize shift overlap time and contact oil pressure of the clutch. The control strategy of clutch was verified by simulation. The simulation results showed that the gearshift parameters chosen with the optimization algorithm were less affected by the change of tractor traction load, and the transmission output speed was transitioned smoothly. It can reduce the negative output torque generated, which avoided tractor deceleration or power transfer interruption during gearshifting, and improved the shift quality.