Numerical simulation was carried out to investigate the flow field and film cooling characteristics of a single cylindrical hole with crossflow and rib turbulators in the coolant supply channel. Three-dimension N-S equations were solved with unstructured mesh and realizable k-?? model. The effect of three kinds of rib angles (60??, 90??and 120??) on the flow field and film cooling effectiveness is studied. The results show that the flow field becomes complicated because of crossflow and ribs. And the flow structures in the film-cooling hole and in the hole exit are controlled by the angle of ribs, which also changes the distribution of film cooling effectiveness on outer surface. The film cooling effectiveness appears to be the highest at rib angle 120??, and the lowest at 90?? rib angle.