Rain, a common weather hazard for aircraft, is one of the major causes of several catastrophic flight accidents. Stealth aircraft commonly employ S-shaped inlets, which are frequently subjected to extreme external environmental effects like rain during mission execution. The present work employs an Eulerian–Lagrangian two-phase flow approach to systematically investigate the effect of rain on the aerodynamic performance of an S-shaped inlet. The computational fluid dynamics method is validated by experiments. The results indicate that rainfall intensity, raindrop size distribution, and angle of attack affect the aerodynamic performance of the S-shaped inlet. It is found that the stall angle of attack for the inlet aerodynamic performance is 17°. Smaller-sized raindrops are more likely to form a water film on the inner wall surface. Furthermore, the larger the angle of attack, the greater the maximum height of the water film. Larger-sized raindrops are more likely to splash into several secondary droplets, forming ejecta fog near the wall surface. These results are valuable for understanding the influence of rain on the aerodynamic performance of an S-shaped inlet.