It is imperative to implement advanced blade cooling technologies to ensure the seamless functioning of aeroengine turbine blades in high temperature environments. The mainstream flow is a pivotal factor influencing the film cooling efficiency of turbine blades. In this paper, the influence mechanism of the main-stream flow on the film cooling efficiency of turbine blades under different main-stream Reynolds numbers and mass-flow ratios is thoroughly investigated. The distribution laws of the cooling efficiency on the pressure surface and the suction surface, as well as the changes in the flow velocity of the central section of the blade, are elaborated in detail. The findings of the research indicate that when the mass-flow ratio is fixed, the cooling efficiency is higher under conditions of a lower mainstream Reynolds number. As the mass-flow ratio increases, the influence of the mainstream Reynolds number on the cooling efficiency gradually weakens. The cooling efficiency on the pressure surface experiences a decrease, while that on the suction surface initially decreases and subsequently increases. Furthermore, an increase in cold air-flow results in a greater accumulation of film in the middle-height region of the blade. This phenomenon enhances the cooling efficiency in this specific area. However, the enhancement of cooling efficiency along the upper and lower wall surfaces is not substantial.