For the problem of non-linearity and time-variable of the topography detector-milling cut depth electro-hydraulic position servo system, a control method for the system based on BP neural network PID was put forward, a BP neural network PID controller was designed. And the model of the topography detectormilling cut depth system based on Matlab was simulated. Simulation results show that compared with the regular PID control method,the BP neural network PID control method possesses better dynamic characteristics and following behavior,which is an effectively controlling strategy.