Two-dimensional (2D) unsteady numerical simulation has been applied to studythe effect of the variation in relative circumferential positions of rotors on the performance of alow speed compressor. The result shows that the variation will change the relative position ofupstream rotor wake to the downstream rotor as well as the periodic and turbulent velocityfluctuations on the airfoils. When the upstream rotor wake impinges upon the leading edge of thedownstream rotor, the corresponding stage efficiency will be higher; when the upstream wake istransferred into the mid-passage of the downstream rotor, the corresponding stage efficiency will belower. The proper configuration of the relative position of rotors will cause obvious reduction inthe unsteady aerodynamic effect on the second rotor airfoils and improve the aerodynamic performanceof blades.