With the development of satellite navigation technology, satellite navigation devices such as unmanned aerial vehicles can receive multi-constellation satellite navigation signals. Positioning accuracy of hybrid constellation is needed to evaluate in the hybrid positioning process. The positioning precision of the satellite navigation is related to the equivalent ranging error and the space geometry distribution. Different receivers use different clocks, and the corresponding clock error will be introduced. According to the principle of satellite navigation, this paper analyzes the variance of the positioning error of the hybrid constellation satellite navigation system. Finally, this paper also analyzes the influence of the constellation system which has poor accuracy to the performance of the whole navigation system. The experimental results show that this method is consistent with the experimental results, and it provides guidance reference for the evaluation of the positioning performance of multi constellation navigation system information fusion.