On the basis of characteristic analysis of the sheet metal CNC incremental forming, the problems of current incremental forming method based on contour line motion were proposed put forward, at the same time，an incremental forming method based on helix motion and the algorithm for generation of helix forming path based on STL model were presented. The isometric model of STL model was generated by using vertex offset method, and was intersected with a series of horizontal plane along with the planes that were parallel with the Z axis respectively. Then the points of the intersection lines were obtained which were linked to be the spiral tool path of forming. The case study indicated that the algorithm can generate non-inference spiral tool path of forming. 