Because the unfolded process of three-way conical pipe is complex, the development drawing cannot be completed automatically. This paper introduced a general analytic algorithm about the development of curve oblique based on the thought of symbolic-graphic combination. The equation of two conical intersection line was established by exploring the mathematical model of the skew intersection to the axis of the cone. The intersecting lines in the SolidWorks interface were created by means of VB progamming and were verified through SolidWorks. After setting up flattening curve equation, the development drawing was carried out in the SolidWorks. Thus, the expansion plan of two cones with arbitrary size and skew axises was designed by parametric means on the SolidWorks interface. The unfolding method is reliable and it makes automatic development drawing practical. The results and relevant data also reveal that the algorithm is of fast speed, high precision and strong universality, which can be used for the expansion mapping of a variety of sheet metal parts to facilitate the manufacture of sheet metal parts.