According to the characteristics of the servo system, and based on the control strategy of generalized time varying systems (4695) of model reference adaptive, a method was realized to adjust parameters of PID controller automatically. As the condition, disturbing, loads changed, the output waveform could be obtained according to the disturbance of the given value. Therefore the vector of characteristic parameters was got by the waveform identification device, and the parameters of PID controller could be updated through expert system, and the output response waveform of adjustable system was tending to ideal waveform. Simulation results show that the output can follow the input position change rapidly, steadily and accurately, and it has strong anti-interference ability as well.