Abstract: Using numerical simulation of unsteady flow fields, the impact of rotor blade tip clearance on turbine efficiency was analyzed for an integral turbine disk. From the perspective of the underflow and leakage introduced by tip leakage flow, the mechanisms of airflow losses due to underflow, leakage, and their coupled effects were studied. It is found that underflow losses are caused by the transition of boundary layer flow, leakage losses result from the reduction of airflow directly involved in work, and the coupling of underflow and leakage constitutes a secondary flow loss. By quantifying the total loss of tip leakage using turbulent kinetic energy, it was indicated that tip leakage flow not only affects the flow field at the blade tip but also influences the flow fields at the blade midsection and root. As the tip clearance increases, the turbulent kinetic energy intensifies and the area of high turbulent kinetic energy regions expands,suggesting an increase in leakage losses and a corresponding decrease in turbine efficiency.