This paper researched the forming theory of the cutting tools with helical teeth and complex surfaces. Deduced the nonlinear equations of the movement of NC system to generate such tools, presented the way to find the solution of the equations, calculate the cross section graphics of the teeth profile and made computer simulation for NC machining. In the former research, the position of the work, the point to be machined, and the position of the grinder are undetermined. They must be solved out by a group of mathematical equations, so that the method can be called as analytical method. In this paper, the position of the work, the point to be machined on the work, are deliberately determined before hand, while the position of the grinder is determined by solving a group of mathematical equations. Because of these, this method can be called as the half analytical method, or the half-forming method. The cutting edge A is deliberately turned to special position, some kind like the forming method, while contact point on the cutting edge B is determined by the contact condition, so that this method can be also called as half- forming method. The concept of this method is very clear, the mathematical form is very simple, and the calculation is very easy.