In order to eliminate the extraneous force of the system and enhance the servo accuracy, dynamic capability and stability, put forward the PID & IMC complex control method. Introduce the structure and working principles of the electric control loading system. Analyze the mechanism of production of extraneous force by setting up the mathematic model and simulating it, and to pitch channel, for example, using step response and sinusoidal response to test validation. The results indicate that the complex control method can lower the influence of extra force and enhancer tracing capability of the system.