Abstract: The present paper makes an attempt at improving the design calculation method of radial impellers through account for viscous property of real gas. Three parts are covered by this paper. The first part gives viscous fluid flow equations in turbomachines in its full tensor form and hereof, its velocity gradient form along artitrary curved direction. In the second part the viscous flow equations and its solution method are outlined for pure radial impeller. Features of the simplified model and the treatment of boundary conditions are emphasized in description. The last part briefs the encouraging calculation result and analysis of a typical example.