Taking the NURBS surface expanding as theoretical basis, the control of the path and the Boolean calculation as basic methods and commercial high-level 3D software as a tool, the problems of the adjustable elbow sheet metal lofting and virtual machining CNC cutting were studied. The accurate physical model of the elbow was acquired by means of solid body surface reconstruction. The correctness of the expansion method was verified through the analysis of the radial and tangential errors of the surface. Combining the secondary development function of CATIA V5 with Excel software, the virtual simulation machining system of the elbow sheet metal lofting was constructed.