Abstract: This paper is a successful trial of an approximately constant reaction stage designed by through-flow streamline curvature method for the first time tension splines.The tip to root reaction difference within 0.1 is attained mainly by the nozzle vanes with positive lean angle of 15° at leading edge and a reverse to usual exit angle twist of 11.6°.To avoid undesirable tip clearance increase in hot running state which would lead to excessive leakage loss,the shroud diameter is kept essentially constant with only a slight taper from nozzle inlet to axial clearance mid-section and then turning outward to the rotor shroud constant diameter.The variations of main gasdynamic parameters,total pressure loss coefficients and stage efficiency along the blade height are shown in figures together with those for a corresponding conventional stage of same meridional geometry for reference purpose which is seen giving even a little (0.20%) higher efficiency.Nevertheless,owing to lack of accurate loss model,especially in regard to leakage loss and shock loss,the efficiency results including their comparison are subject to experimental verification,although the design of constant reaction in general is credible.