Abstract: According to strict theory of similarity,the modelling conditions for model experiments on cooling blades or vanes of a gas turbine are obtained from a necessary set of differential equations and single valued conditions.It is shown that when the pressure in modelling is lower than that in the actual turbine,the temperature in modelling must be lowered simultaneously in order to maintain the criterion on pl/μc PT for cooling air and for gas invariant.Therefore,it is necesary to increase the pressure and to decrease appropriately the temparature in modelling tests for the blades and vanes of high pressure turbines with high pressure ratio.