Abstract: In order to reveal the influence of the winglet width of the suction side on the aerodynamic performance of the counter rotating axial fan, the flow field structure of the downstream rotor with different tip loading was studied numerically in this paper. The results show that the aerodynamic efficiency and total pressure rise of the counter rotating fan can be effectively improved by using the suction surface winglet. As the width of winglet increases, the performance improvement effect is more significant. When the tip loading on the rotor increases, the flow field in the tip region deteriorates, and the aerodynamic benefit obtained by using the winglets increases gradually. The main mechanism of this phenomena is that the winglet weakens the strong primary tip leakage vortex into two separated small tip vortices, and greatly reduces the strength of the primary tip leakage vortex.