Abstract: The error modelling method is one of the most important technologies for NC machine error compensation. Based on the characteristic of NC machine, a more accuracy error medeling method, which is widely used, is introduced. Meanwhile, a geometric description method for multi-body system with existed movement error is presented and the movement restrain equation of NC machine is derived. The result from related research shows that this conclusion can be applied to the NC machine error compensation and the cutter line calculation. The experimental results show that the new error modeling method presented in this paper is effective.