Abstract: Based on analyzing the principle of pipe end CNC cutting and spatial analytic geometry, this paper obtained a pipe-pipe intersecting line mathematic model. On this foundation, combined with other research results, it puts forward a pipe end mating face model. Compare with the traditional ones, the model avoids complex matrix transformation of spatial coordinates, and is more simple and pellucid, which makes it easily to be programmed. Besides, by pointing out the disadvantages of the common dividing method, the paper developed a compared dividing method to improve fitting precision. The model and methods described has been tested by AutoCAD VBA program simulation, and been applied in developing related software.