Abstract: The flowfield in axial compressor is characterized by unsteady vortex flow due to the relative motion of the blade rows.The upstream unsteady wake flow changing periodically is responsible for the airfoil aerodynamic efficiency and thus for the overall performance of the aeroengine.This paper examines the influence of such unsteadiness of upstream wake impact on the development of vortex sheets of downstream blades in a highly loaded HPC(High pressure compressor).The results of this study indicate that the temporal-spatial structure of wake impact effect in multistage turbomachinery flowfield could be more deeply understood when the unsteady processes are considered through the interaction of respective vortex sheets.The results suggest that the performance change is corresponding with temporal-spatial structure of the flowfield.The vortex sheets interaction of upstream weak and downstream blades might reduce the loss.It is the frequency of the vortex shedding alternately at the trailing edge that couple with the upstream weak passing frequency,instead of the frequency of leading edge separated vortex instability.