Abstract: In addressing the issue of adjusting the axial velocity density ratio in experiments with supersonic compressor planar cascades, numerical simulations were employed to investigate the impact of end-wall slotting on the flow field of the supersonic compressor cascades. This study analyzed the challenges of simulating two-dimensional flow in the mid-section of three-dimensional linear supersonic compressor cascades and conducted comparative research on the effects of different end-wall slot sizes (slot heights of 0, 0.5, 1.0, 2.0, and 4.0 mm) on the corner separation flow of the compressor cascade. The effectiveness of the end-wall slotting method in regulating the axial velocity density ratio in the mid-section of the cascade and controlling flow separation in the end region was revealed. The results indicate that when the outlet is subsonic, the unslotted three-dimensional linear cascade exhibits intensified end-wall region separation, causing the axial velocity density ratio in the mid-section to sharply rise to above 1.2, while the inlet Mach number decreases significantly from 1.58, deviating from the characteristic of a two-dimensional cascade. End-wall slotting can effectively reduce the axial velocity density ratio in the mid-section of the supersonic compressor cascade, although an optimal gap value exists. A slot height of 1 mm can effectively control the axial velocity density ratio to below 1.05; the blade surface isentropic Mach number distribution, total pressure loss, and exit Mach number characteristics all return to the level of two-dimensional flow. Increasing the size of the blade slots (e.g., 2 mm or more) enhances the secondary flow in the end region, inducing flow separation in the upstream corner and increasing the spanwise extent of the trailing edge vortex downstream, which leads to greater flow blockage in the end region, causes overflow on the pressure surface, and produces adverse effects. Therefore, the end-wall slotting can provide a more reliable methodological basis for the variable-pressure-ratio cascade testing of a supersonic compressor airfoil in an aircraft engine.