Effect of the slashface leakage on the gas turbine blade endwall film cooling and heat transfer performance under three endwall misalignment modes (aligned, cascade and dam) is numerically investigated using the method of solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with the SST k - omega turbulence model. The numerical calculations are conducted with four coolant momentum flux ratios (I) of 0.48, 0.96, 1.42 and 1.87 under three different endwall misalignment modes. The computational results indicate that for the aligned mode, the fore part endwall (z/C-ax < 0.4) cooling effectiveness reaches the maximum when I = 0.96 and the coolant coverage on the back part endwall moves upstream with the increasing coolant momentum. The main high Nu regions concentrate at the back part endwall and the small high heat transfer region at z/C-ax = 0.2 increases the endwall heat transfer coefficient by 8% and 3% for I = 1.42 and 1.87, respectively. As for the cascade misalignment mode, the cooling effectiveness of the fore part endwall decreases sharply with the increasing I. There are mainly two high Nu regions at the fore and middle (0.4 < z/C-ax < 0.7) part endwall caused by misalignment induced vortex. There is also a low Nu region near z/C-ax = 0.9 caused by horseshoe vortex separation, and it can decrease the endwall heat transfer coefficient by 10%. For the dam misalignment mode, the cooling effectiveness is lower but distributes more evenly obstructed by the dam. The horseshoe vortex reattaches on the back part endwall (z/C-ax > 0.7) and causes a high Nu region near z/C-ax = 0.9 that increases the heat transfer coefficient by 20%, which also leads to a cooling protection failure region. Another severe high Nu region at the middle part of the endwall is brought by the separation vortex reattachment. (C) 2018 Elsevier Ltd. All rights reserved.