Abstract: Abstract The flow in turbomachiney is inherently unsteady, so investigating the unsteady interaction between the downstream pressure field and the end-wall flows is very important for improving the performance of lowaspectratio, highloaded turbine. This paper presents the results of a numerical study of the interaction between the endwall secondary flow and tip leakage flow of the rotor and the downstream potential field of the stator in a low-aspect-ratio, subsonic turbine. The flow diagrams of transient results were analyzed in detail. The results indicate that the entropy rise and the efficiency at the exit of the rotor blade showed a significant periodic variation due to the unsteady interaction of the downstream pressure field. The periodic variation of the rotor performance is due to the unsteady interactions of the downstream pressure field with the secondary flow vortex and the tip leakage vortex, which has been interpreted using the theory of kinematic vortex transport.