In this paper, a variable particle separator is designed for a C-shaped inlet. The separation flow path is switched by rotating a rotatable wall which is a portion of the intake wall. The two-phase model and CFD method are used to calculate and analyze the particle separation efficiency of the variable particle separator, the total pressure recovery, and the total pressure distortion of the intake. The effectiveness of the variable particle separator in capturing particles of various sizes is validated. When the rotation angle of the rotatable wall is not greater than 60 degrees, the particle separation efficiency remains at a high level and is hardly sensitive to the rotation angle. However, the aerodynamic performance of the intake always deteriorates as the rotation angle rises. The calculation results also indicate that a larger size of the rotatable surface is conducive to the separation of larger particles with higher inertia, while a smaller area is more suitable for small particles due to their higher flowability. Based on comprehensive considerations of the performances of the intake and the particle separator, as well as their installation on the aircraft, the position and size of the rotatable wall are α1 = 25° and α2 = 45°, respectively. The rotation angle of the rotatable wall is 15°.