In order to solve the problems of high energy consumption, air duct accumulation and local wear of pendulum mill, the structural design scheme of air inlet duct (including volute and air duct blade) was studied. Based on coupling simulation techniques of fluid dynamics, multiphase flow and discrete element, Numerical simulation of the internal wind field and particle field of the pendulum mill were carried out. The response surface simulation tests of volute profile, blade Angle and blade number were also performed. The results show that optimizing volute profile is beneficial to reducing pressure loss and equipment energy consumption, and reasonable selection of blade angle and blade number is beneficial to reducing the non-uniform coefficient of air duct and regulating flow field. Based on the multi-objective optimization of pressure loss and non-uniformity coefficient, the optimal scheme of air duct structure is determined as: volute 2, blade number 18, blade angle 55°. The finished product collection efficiency of the optimized scheme is 95.3%, which is 13.4% higher than that of the original scheme. The simulation results are in good agreement with the field experimental data, which can provide guidance for the optimization and energy-saving design of pendulum mill.