Abstract: The discharge coefficient of the plain circular holes and the film cooling holes were investigated with numerical simulation method.The relation of the discharge coefficient to the geometrical and the flow parameters were studied.Results of the proposed formula for plain circular hole were compared with the experimental and theoretical data, and they agreed well.Sometime slot is used instead of circular holes to simplify the geometry of the combustor.The determination of gap’s equivalent area was also investigated.All calculated results indicate that numerical simulation is a feasible,simple and effective method to determine the discharge coefficient of the gas turbine combustor air holes.