Weibull distribution shows good flexibility and applicability to the reliability distribution of various forms, and the failure interval of the wind turbine rotor system also obeys the Weibull distribution. Therefore, the Weibull distribution can be used to establish the fault distribution model of the wind turbine rotor system. However, in the calculation of Weibull distribution parameters, the conventional parameter calculation mainly considers the calculation workload or the accuracy of the solution, ignoring the total deviation and effectiveness of the model, resulting in a large deviation between the calculation results and the actual operation of the wind turbine rotor system, and thus affecting the accuracy of reliability evaluation. Inaccurate reliability assessment results can lead to incorrect decisions and planning, increasing maintenance costs. To solve this problem, a calculation method of Weibull distribution parameters based on K-S test error square sum minimum method is proposed in this paper, which can effectively solve the problem of large calculation error of Weibull distribution parameters, and the fault data of wind turbine variable pitch system is taken as an example.