To identify the law of aerodynamic interactions of contra-rotating propellers (CRPs) and improve their aerodynamics, this study investigates the aerodynamic interactions of 4 CRPs (six blades in front and six in back) with different stage spacings using the Reynolds-averaged Navier-Stokes (RANS) equations-based method. The results showed that the CRP whose stage spacing was 0.25 times the propeller diameter delivered the highest average efficiency and that the aerodynamic interactions between the front and rear propellers decreased as the spacing widened, and compared with the rear propeller, the front one was more sensitive to stage spacing due to the aerodynamic interaction-generated thrust fluctuations. It can be seen that stage spacing exerts a significant effect on CRP aerodynamic interactions. Therefore, choosing an appropriate stage spacing in CRP design is of great significance to enhance its aerodynamics.