The numerical simulation method is used to solve the problems of pipe bending manufacturing such as die with fine cracks, ovality of pipe. The fan-shaped die is welded with steel plate in circle and rib in radial direction by the analysis of structural deformation. The optimal design is provided with ovality of pipe as object variable and sliding slot dimensions as design variables. Compared with experiential shape groove of slot, ovality of optimized slot decreases about 10.5% in average. It greatly reduced the production cost using computer simulation method to replace a lot of experiment improving tube-bending production.