Abstract: There were two points in the character-curve whose errors were equal to the required tolerance of the contour. And in the cutter surface and the to-be-machined surface, the corresponding points existed. Based on the phenomenon, a novel algorithm was brought forward. It was mainly to optimize the tool position under the condition of fixing the errors at the end-points of effective-character-curve-segment (the part of character curve within the tolerance zone). The torus cutter was first positioned by the two end-points. Then by adjusting the distance between the two points and the rotating angle around the line connected to the points, interference could be avoided, and optimization of the tool-orientation could be achieved. A program was developed to verify the validity of the algorithm in avoiding interference and realizing maximal path interval, iso-scallop tool path planning.