Considering the variety of alternators’type and the changeability of test condition，an improved BP neural network PID controller is designed for the alternator servomechanism. During the process of test condition parameter improvement，PID parameters are adjusted adaptability and on line. This approach exhibits more significant dynamic performance and may improved greatly on efficiency of alternator product line. The improved BP neural network PID controller’s composition and it’s arithmetic are described. The simulation results on the application of adjusting alternater’s speed in the servomechanism show that this way is effective.