The film cooling mechanism and characteristics of a row of cylindrical holes with branched jet injections were investigated by numerical simulation. Three geometries for the branched jet injection holes and four blowing ratios were considered. The results led to the following conclusions: (1) when additional branched jet injections supplement the primary holes, the kidney vortices are suppressed, and film lateral coverage is enlarged, which improves the film cooling effectiveness; (2) suppression of kidney vortices from the primary holes is due to anti-vortex and coolant-distribution actions by the additional branched jet injections; (3) when the exit of the branched jet injection holes is located in line with the primary film cooling holes, a lower heat transfer coefficient ratio and higher film cooling effectiveness are achieved; (4) the film cooling effectiveness is clearly improved by additional branched jet injections under higher blowing ratios.