Endwall is one of the critical regions to perform film cooling for gas turbine because of not only the increase of turbine inlet temperature but also the complicated secondary flow. Typical endwall film cooling configuration includes leakage slot at combustor-vane interface and discrete cooling holes on the wall. This paper mainly studied the effect of endwall step on the cooling performance of downstream cooling holes. The combustor-turbine interface in this paper is a kind of backward-facing step, causing an interrupted slot. The detailed characteristic of the interrupted slot has been investigated in the previous study. Three dimensional Reynolds-averaged Navier-Stokes equations with shear stress turbulence model (SST) k-omega was solved to perform the calculations of endwall film effectiveness. The adiabatic film effectiveness on the flat endwall was compared with that on the stepped endwall with and without the interrupted slot. Results showed a significant impact of the endwall step on the adiabatic film cooling effectiveness. Coolant jet downstream of the step is split into two parts due to the effects of step vortex (SV) and cross flow. Detailed flowfields in spanwise, pitchwise and axial planes explain the formation and development of secondary flow near the cooling holes. For a range of blowing ratio from 0.6 to 1.2, increasing the blowing ratio of cooling holes deteriorates the adiabatic film cooling effectiveness upstream and downstream of the cooling holes due to the jet liftoff. It is found that cooling effectiveness is strongly dependent on the axial position of the hole. Placing the cooling holes downstream at leading edge plane of the cascade little effect of the step vortex on the film effectiveness and, subsequently, relatively uniform coolant coverage was observed on the endwall. (C) 2019 Elsevier Ltd. All rights reserved.