The shift system of electronic automatic transmission was analyzed, and a mathematic model of the shifting process was set up. The model could be used directly for shifting process control. With the model the shifting process was also analyzed, and the rule of shifting process was obtained. The process of the clutch applies and exhaust was analyzed. Through adjusting the pressure by using PWM to control the solenoids, the pressure was controlled in good conditions. Trough the research, the system used the open-loop control during the fill-time phase, faxed ramp rate control during the second phase and closed-loop control during the third phase by using PID control strategy. At the same time, the electronic engine was used to adjust the engine speed to acquire the better quality of shifting-process. Finally, though a bench test, the control strategy of shifting process of the electronic automatic transmission was obtained.