The pressure-side cutback is used to design the trailing-edge film cooling. Previous studies have demonstrated the strong unsteady film mixing between the mainstream gas and the slot coolant, resulting in rapid deterioration of the film cooling effectiveness on cutback surface. The shedding vortexes formed by the clockwise and counter-clockwise structures induced by the mainstream and slot coolant shear-layer account for the strong blending. The RANS/LES hybrid turbulence model (DDES) has been proved to capture the locally unstable flows well. The flowfields and temperature of the cutback under eight blowing ratios Mslot = 0.3 ∼ 1.2 are simulated. With the increasing of blowing ratios, the counter-clockwise structures induced by the slot coolant shear-layer are strengthened to dominate the shedding vortexes gradually, which is corresponding to three kinds of coherent structures. Under low Mslot = 0.3 ∼ 0.5 dominated by clockwise structures of the mainstream, the effectiveness increases. Under middle Mslot = 0.5∼0.75 dominated by both clockwise structures of the mainstream and counter-clockwise structures of the slot coolant, the effectiveness decreases. Under high Mslot = 0.75∼1.2 dominated by counter-clockwise structures of the slot coolant, the effectiveness increases again. To weaken the blending at cutback, the pressure-side film hole with Mhole = 0.4 is arranged close to the cutback to rebuild the mainstream shear-layer. The weakened mainstream shear-layer and the assistant hitting of the hairpin vortexes from the hole injection can weaken the strength of the shedding vortexes at cutback, contributing to the improvement of the effectiveness on cutback surface under low Mslot = 0.5 and middle Mslot = 0.75. Under high Mslot = 1.0, the less influence of the hole injection on the shedding vortexes dominated by the slot coolant counter-clockwise structures accounts for slight improvement. Finally, FFT analysis is obtained for two configurations.