Abstract: The unsteady flowfield of the turbine stage was investigated numerically under different axial gaps,and the influences of the axial gap on the aerodynamic loss and the flow unsteadiness were discussed.Results show that the flow unsteadiness in the turbine stage becomes stronger with the reduction of the axial gap,and the corresponding flow becomes non-uniform.The total pressure loss coefficient of the turbine with the larger axial gap is bigger than that with the design axial gap.The reason is that the mixing distance between the wake and the main flow becomes much larger.Due to the much stronger flow unsteadiness under the smaller axial gap,the corresponding aerodynamic loss of the turbine stage is larger.There exists an optimum axial gap to minimize the aerodynamic loss.