Abstract: In order to control flow separation in a diffuser and improve energy efficiency, this paper investigates the control effect of vortex generators（VGs） on separated flow in a diffuser. Based on the Reynolds Stress Model (RSM), a comparative study is conducted on the effects of three types of VGs—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 a three-dimensional asymmetric diffuser. The results show that the R-type and Vu-type VGs can effectively suppress flow separation and improve the pressure recovery coefficient, while the Vd type may aggravate separation, leading to a reduction in the pressure recovery coefficient. In terms of reducing the diffuser’s distortion index, the R type performs better. By comparing 16 types of VGs, it is found that only the Vu1 type can effectively improve efficiency, and the optimal installation height is estimated to be within the low-profile range of h/H \lt 0.2. This study provides a reference for the performance optimization of diffusers and the design of the VGs.