An increasing number of large wind turbines with a variable-speed variable pitch control mechanism are developed to improve the response speed of wind turbines and get maximum active power .Designing a reasonable pitch control system requires both a good control scheme and a more accurate wind turbine model. Base on the analysis of wind turbines’ principle, a local linearization model of wind turbine is built by using linearization method of small deviation in this paper. The model’s inputs are the data of wind speed and pitch angle, and the output is the active power. The accuracy of the model is verified by studying the active power output of wind turbine under different circumstances in which the pitch angle changes with a constant wind speed and the wind speed changes with a constant pitch angle. At the same time, this paper provides pitch control program based on internal model control after analyzing the disadvantages of PID pitch controller. When the wind speed is beyond the rating, the active power can be limited reasonably around the power rating of wind turbines by adjusting the pitch angle.