In order to solve the problem that the optimal design of the gravity dam takes the section size as the only design variable and lacks consideration of the influence of material properties on the optimal design of the gravity dam, this paper studies the multi-objective optimization method of gravity dam comprehensively considering the economy and seismic safety. Firstly, the multi-factor evaluation system with comprehensive economy and safety indicators is put forward; secondly, based on the ABAQUS software, the static and dynamic model of the gravity dam are analyzed, and then the variable-weight efficiency coefficient method is used for the quantitative evaluation based on the calculation results of finite element analysis; finally, the XGBoost-PSO algorithm is used for optimum seeking to obtain the final optimization scheme. The validation results of real projects show that the economy and seismic safety indexes of the optimized scheme have been significantly improved compared with the initial scheme. Compared with the traditional single-objective optimization method, the economic and safety indexes of the multi-objective optimization is more suitable for gravity dam projects with high seismic safety requirements.