The mathematic model of deviation angle distribution of uniform thickness conical surface windshield glass was deduced based on the theory of ray-tracing, and a method for establishing the engineering model of angle of deviation was also proposed.Based on which, an approximate model with high-precision was developed by using least square method.The model is applicable for real-time compensation of the relative deviations for the onboard software, which has been applied in a certain type of airplane successfully.