Due to high forming load and serious die wear, the large diameter straight bevel gear is seldom to manufacture by forging. A new forming method is proposed to manufacture the straight bevel gear by a specific die with a flash and a boss, and the forming load and die wear are regarded as the optimization targets. Die with a flash is significant to reduce the load and die wear. However, the small-end section and large-end section of tooth surface is incomplete filling. Therefore, a flash and a boss are combined to design in die to make sure low forming load and good precision accuracy. Firstly, according to the load and die wear results of traditional forging process by Deform-3D, a flash and a boss are designed in the final forming die of three and two steps, and the two-step process is determined by the comparison of load and die wear. Secondly, test plans of the pre-forging and final forging dies are carried out using Taguchi, and the structure of the pre-forging and final forging dies are analyzed and optimized. Thirdly, test plans of the pre-forging and final forging process parameters are established by response surface analysis (RSA), and the optimal scheme of parameter is determined. Finally, physical experiments and practice forging are proceeded to certify the optimal results of finite element (FE), and the results of experiments and FE have a good consistency.