Abstract: This paper persents a method for aerodynamic design calculation of axial gas turbine stage with the mixing of cooling air.The mass flow mixing and the energy mixing of the cooling air with the main gas flow are considered directly in the continuity and the energy equations,while the momentum loss resulting from the mixing is considered indirectly.The losses of blade rows and their distributions in the radial direction are determined by means of the loss models provided in the paper.The influences of different cooling types of blades and the non uniformity of the inlet total temperature and total pressure in the radial direction have been considered in the calculation program.The method could be applied to multi stage air cooled gas turbine.The basic calculation method adopted is the streamline curvature method.As an example,a design calculation of an axial turbine stage are presented.The calculation results show that the effect of the cooling air mixing on the turbine efficiency is significant.