With the development of CAD/CAM, reverse engineering, geometric modeling, animation and computer graphics. In the past fifty years, many kinds of spline curve fitting methods have been produced. But, to authors knowledge, quality evaluation criterion about different spline curves are still not established and there is a lack of a comparing standard for analyzing different spline curves. Two spline curve fitting method comparing theorem is given and several various spline curves affecting factors are analyzed in this paper. Some comparable results are obtained by using the proposed quality evaluating theorem to different spline curves.