As a common transmission equipment in various engineering practice,reducer is mainly used to realize torque transferring and speed matching.Taking the reducer of belt conveyor as the object,static analysis was carried out on its highspeed shaft by using ANSYS Workbench,and the design objectives of lightweight and maximum material performance were put forward.Combined with multiobjective optimization theory,response surface model was built to optimize the size of dangerous section.The results show that the optimized gear shaft mass decreases by 171%,and it still meets the strength and stiffness requirements.It provided reference for optimal design of reducer under other working conditions.