Abstract: A three dimensional,multigrid potential flow computation method is developed to analyse subsonic flow in steam turbine nozzle guide vane.In order to reduce the large secondary losses in the first annular nozzle guide vane with very small aspect ratio of 0 26 in a 300MW steam turbine,both tip endwall contouring and combined lean blades are used in the new design.Experimental investigation shows that the mass weighted loss coefficient of the new nozzle guide vane is 42 percent less than traditional radial one.The agreement between the measured and calculated results of the pressure distribution on the blade surface in the annular nozzle guide vane is very good.The present study is a success in developing fully 3D steam turbine nozzle guide vane with tip endwall contouring and combined leaning blade.