Abstract: The vigorous development of China's wind power industry is inseparable from the support of national policies. If the wind power industry wants to rely on market mechanisms to gain a firm foothold in the fierce competition and achieve sustainable development, it must give full play to its own price advantage, which is the key to the development of alternative energy into the mainstream energy, so it is crucial that reducing the cost of wind power and improving the efficiency of wind power generation. The power generation efficiency of wind turbines is closely related to the aerodynamic performance of airfoils, and it is one of the key technologies to increase the utilization rate of wind turbines and improve the efficiency of wind power generation by optimizing the aerodynamic performance of wind turbine airfoils. The S809 airfoil for wind turbine was taken as the research object for the study of optimizing the aerodynamic performance, measures were adopted to make a slit on the trailing edge of the airfoil, and the change of aerodynamic performance of the trailing edge slit airfoil was studied by numerical simulation method at a Reynolds number of 500,000. The results show that in the attack angle of 5°~10°, the drag coefficient of slotted airfoil increases significantly compared with smooth airfoil. In the range of small attack angle of 0°~13°, the lift coefficient of the airfoil decreases due to the slit at the trailing edge. When the Angle of attack is 14°~20°, the trailing edge slit can effectively improve the lift coefficient of the airfoil, the drag coefficient is almost unchanged, and the lift-to-drag ratio can be increased by up to 11.4%. By analyzing the streamline diagrams and flow field cloud diagram of the airfoil at 8° and 18° attack angles, it is found that the trailing edge slit delays the flow separation point and inhibits the flow separation area, thus improving the aerodynamic performance of the airfoil.