Numerical simulation was carried out to investigate the film cooling mechanism of the crescent-shaped block & plasma actuator structure. With CFD method, flow field characteristics, temperature characteristics and cooling effectiveness were analyzed for different film cooling structures: the common circle-hole, crescent-shaped block and plasma actuator film cooling structure. The results show that in circle-hole film cooling structure, counter-rotating vortex pair(CRVP), which lifted the cooling flow and entrain the hot flow, was formed, therefore the cooling effectiveness was the lowest. In the plasma actuator structures and crescent-shaped block structures, anti-CRVP, which restrained the scale and strength of CRVP, was formed. Compared to that with common circle-hole cooling structure, the film cooling effectiveness is improved a lot both in lateral and streamwise. In the crescent-shaped block & plasma actuator structure, the anti-CRVP reached its maximum, therefore significantly improving cooling effectiveness in the area between the holes and generating the best cooling performance.