Abstract: Taking advantage of nolinear finite element analysis technique and bilinear material model, stress distribution characteristics of big-diameter straight tee in two stress concentration ares is analyzed.By means of VS2005, ANSYS and Pro/E, optimized module for straight tee is developed and rational structure for straight tee is obtained, which can effectively decrease stress concentration level of straight tee.Relationship between pipe thickness, branch pipe's radius and optimized structure parameters of straight tee is analyzed, which offer a reference basis to process parameter optimization of hot press molding for high-grade steel straight tee.