With the booming performances of the gas turbine engine, the turbine vane of the gas turbine engine experiences more extreme thermal environment with supersonic flows. The film cooling applied in the supersonic flow condition has essential difference from that used in the subsonic flow condition in the flow characteristics and cooling effectiveness. This article focused on the film cooling of two parallel flows (primary flow and coolant flow) with supersonic or subsonic velocity, respectively. The results show that: on the condition of supersonic primary flow and subsonic coolant flow, the coolant flow with lower momentum is sheared and dragged by the higher momentum primary flow because of the viscous property of fluid. At the meantime, the thermal and momentum of the primary flow transfers into the coolant flow rapidly. It causes the great damage of the film coverage, and the decrease of the cooling effectiveness dramatically. In contrast, on the condition of supersonic primary flow and supersonic coolant flow, the film coverage of the supersonic coolant flow can last further far than that of the subsonic coolant flow on the same blowing ratio. The turbulence kinetic energy seems to be depressed by the shorten of velocity difference of two supersonic flow. Therefore, the cooling effectiveness is enhanced by 45% for the supersonic primary and coolant flow.