Abstract: According to the intake characteristics and the structural constraints of turboprop engine, a design method of the S-duct intake is proposed, which enables the flexible design requirement of the inlet tract while satisfying the structural constraints. With the design method, influences of the design parameters on the aerodynamic performance of intake are analyzed by the numerical simulation technique. The results demonstrate that both the total pressure loss and distortion coefficient decline with the increasing of the intake area ratio or the inlet spread angle, and the shroud line has a dramatic effect on the distortion coefficient. Finally, the aerodynamic design of a turboprop S-duct intake is accomplished by combining the above research findings. The simulation result indicates that there has been a significant improvement in the performance of turboprop intake, the total pressure loss and distortion coefficient reducing to 0.81% and 0.06 respectively, which validates the effectiveness of S-duct intake design method.