Abstract: In order to control flow separation in a diffuser so as to improve the energy efficiency, this paper studies the control effect of the vortex generator on the diffuser separation flow. Based on the Reynolds Stress Model (RSM), the effects of three types of vortex generators (VG), namely the ramp type (R), the vane with upwash type (Vu), and the vane with downwash type (Vd), on the flow field and performance of the three-dimensional asymmetric diffuser are comparatively studied. The results show that the R type and the Vu type VGs can effectively suppress the flow separation and improve the pressure recovery coefficient, while the Vd type may aggravate the separation phenomenon, resulting in a decrease in the pressure recovery coefficient. In terms of improving the distortion index of the diffuser, the R type performs better. By comparing 16 types of vortex generators, it is found that only the Vu1 type can effectively improve the efficiency, and the optimal installation height is estimated to be in the low-profile range of h/H < 0.2. This study provides a reference for the performance optimization of the diffuser and the design of the vortex generator.