Abstract: This paper establishes a power generation assessment method that takes into account the effect of wind shear by using the concept of Rotor Equivalent Wind Speed（REWS）. Firstly,this paper establishes a wind shear simulation method for wind turbines according to the CFD method. The reliability of the method is verified by the actual wind farm case. Secondly,this paper analyzes the error of traditional power generation assessment method through the actual wind farm case. This error is as high as 4.33% at the turbulence intensity of 0.14 and as high as 4.51% at the turbulence intensity of 0.18, so it cannot be ignored during the assessment process. Finally,this paper establishes a new power generation assessment method by using REWS to define the power curve. The wind farm verification results show that,the new method reduces the power generation assessment error caused by wind shear from 4.51% to 0.62%,which has high assessment accuracy.