Engineering vehicles mainly include loaders, excavators, bulldozers, forklifts, etc. They have a wide range of applications. The AT transmission studied in this article is mainly used in loaders. To enhance the dynamic performance and service life of engineering vehicle transmissions under extreme working conditions, a multi-objective optimization method considering the dynamic performance and fatigue life of the transmission system is proposed. Considering the influence of gear parameters on performance, a parametric design method for gear profiles is proposed for the calculation of gear efficiency and load capacity. A system dynamic model is constructed using the rigid-flexible coupling method, comprehensively considering the gear stiffness, flexible components, and bearing variable stiffness effects, revealing the dynamic characteristics and dynamic load distribution of the system. Subsequently, a fatigue life prediction model for key components is established to quantify the influence mechanism of load excitation on life. Based on the multi-objective optimization framework, with system mass, transmission efficiency, and meshing torque fluctuation as constraint conditions, combined with the performance and life prediction model, an optimization model is established, and finally, the optimal gear design parameters with the best comprehensive performance are obtained. The results show that the comprehensive performance of the optimized AT transmission is improved.