Abstract: A mathematic model based on free trailing vortex theory and lifting-surface theory was developed to describe the ambient airflow by blades and characteristics of wind turbine so as to investigate the aerodynamic behavior of a wind turbine blade. A numerical solution to the model was carried out to obtain the relationship between tip velocity ratio and power coefficient as well as that between wind velocity and power coefficient by introducing the induced velocity between the blades and vortices. Compared with experimental data, it was found that the theoretical results conform basically with the experimental results. Further, compared with the CFD (computational fluid dynamics) method, the free trailing vortex method would get acceptable computational accuracy at lower cost. The results are therefore regarded as available to select the wind turbine position in a wind field and optimize the design of wind turbine control system.