On the basis of internal model PID control method,this paper researches further the servo system of a large telescope for reducing its adjusting parameters in servo control loop. The design ideals of internal model control are introduced and the algorithm of internal model control is discussed. Analysis and simulation results verify that the algorithm simplifies the debug process; and it is feasibility and robustability for high precision application fields. The practicability of this algorithm is verified in an actual project. The application shows that this system runs stably and accurately, and has a few adjusting parameters in servo control system.Also, there is no overshoot while the speed is high and the lowest speed can reach 15″ in stable operation. The technology and methods adopted in the system are practical and worthy to be used.