Double NURBS method is used to construct the surface model of a rotor.The technologies of surface extension,surface intersection and surface trimming are studied.Based on the geometric expression of the NURBS curve,a simple and effective method of curve and surface extension is put forward,and the blade surface is then successfully extended with the tangent vector by repeatedly applying the above method.A simplified tracking approach is adopted to realize the surface/surface intersection,of which one surface is analytic surface and the other is free surface.