Abstract: Three dimensional time-dependent Reynolds averaged Navier-Stokes equations were solved to investigate the unsteady flow in a transonic high pressure turbine stage. The influence of wake and shock waves of the stator vanes was analyzed. Results show that the aerodynamic performance parameters solved by steady/unsteady methods are similar, while the flow patterns are discrepant. The interaction between the upstream wake and downstream boundary and vortexes is marked and lead to the increase in the flow loss especially near the hub of the rotor. And high-frequency-shedding vortexes appear as a result of the interaction of the wake and hub passage vortexs. The stator wake is one of the major reasons that induce the unsteady effect of the rotor flow. The trailing edge shock waves of the stator vanes are considered as another reason. Due to the shock wave/boundary layer interaction phenomena, the distribution of static temperature on the surface of the rotor is influenced and high static temperature is produced periodically. Meanwhile, the distribution of static pressure on the rotor surface changes: the static pressure on the surface rising rapidly behind the shock waves; on the other hand, the shock wave/boundary layer interaction results in the flow separation on the suction side of the rotor. The rotor loading distribution changes periodically as well as the output power of the turbine.