Abstract: Near-space vehicles encounter significant aerodynamic heating challenges. Liquid films are considered a promising thermal protection approach due to their efficient cooling capabilities. This study numerically investigated the liquid film cooling process on an oblique plate at Mach 5. A second-order accurate coupled implicit algorithm was employed to solve the Navier-Stokes equations. The volume of fluid (VOF) method coupled with adaptive mesh refinement was utilized to capture the two-phase flow interface and interphase interactions. An evaporation model was introduced to simulate the endothermic process during liquid evaporation. The characteristic flow field structures during the spreading and evolution of the liquid film on the hypersonic oblique plate surface were analyzed. Furthermore, the effects and mechanisms of coolant mass flow rate, surface tension, viscosity coefficient, and plate inclination angle on liquid film cooling performance were discussed. The introduction of liquid-phase coolant reduced the wall heat flux on the oblique plate by approximately 40%—87%, demonstrating significant cooling performance. The wall heat flux reduction coefficient increases with increasing coolant mass flow rate, surface tension, viscosity coefficient, and decreasing plate inclination angle. This study reveals the interaction mechanism between aerodynamic heating and the cooling liquid film, providing new insights for addressing thermal management challenges in hypersonic vehicle thermal protection systems.