Abstract: Airfoil is the basic element of the airplane wings and turbomachinery design such as wind turbine blades. In order to effectively suppress the flow separation of airfoil surface and improve the aerodynamic performance of wind turbines, bionic fin similar to bird feathers were installed on the suction surface. The flow field structure around the airfoil was studied by numerical simulation. Meanwhile the angle coefficient method was proposed to determine the installation angle of the bionic fin and the noise characteristics of the airfoil were further analyzed. The results show that in the state of the flow separation, the bionic fin at the optimal lift angle effectively prevent the separation from moving forward, delay the stall angle of attack, reduce the size of the trailing edge shedding vortex, and increase the maximum lift coefficient by 21%; At the same time, the main frequency sound pressure level of the fin airfoil is reduced by 23.5 dB, and the total sound pressure level in the circumferential direction shows a dipole distribution and is significantly reduced. The numerical results provide some reference value for the engineering application of the angle coefficient method.