The interaction between rotor and stator airfoils in gas turbine causes an inherently unsteady flow field. Clocking effect, as one of the typical unsteady flow effects, has aroused extensive attention in scholars. Presented study is conducted in a two-stage cooled turbine, with unsteady Reynolds-average Navier stokes(URANS) method employed to investigate the influences of stator airfoil clocking effects on mass flow and efficiency characteristics. Computational results show that the difference of second stage cooling air could be approximately 15.6%, and the amplitude of turbine 41-section efficiency and thermodynamic efficiency fluctuation are 0.33% and 0.26% respectively. Variation of second stage cooling air would impact 41-section efficiency to a certain extent, however, extra profile losses caused by clocking effect play a more important role on turbine efficiency fluctuation.