Objective In response to the current demand for green logistics and the need to reduce energy consumption costs and carbon emissions costs this paper proposed a study on the optimization of vehicle routing in a mixed vehicle fleet under low-carbon goals and explored logistics transportation solutions for mixed fleets. Considering the differences in mileage energy consumption and carbon emissions between the mixed fleet and the fuel-fired fleet or the electric vehicle fleet an optimization model was constructed to minimize fixed costs travel costs energy consumption costs and carbon emissions costs. Methods In this study the particle swarm optimization algorithm was employed in conjunction with the Metropolis criterion to improve algorithm efficiency. Multiple sets of experiments were designed to analyze and compare the differences in driving mileage energy consumption and carbon emissions between the mixed vehicle fleet and a single vehicle type fleet. Results The results demonstrated that the mixed vehicle fleet had significant advantages in reducing carbon emissions carbon emissions costs and operating costs. The mixed vehicle fleet effectively reduced energy consumption and carbon emissions leading to a 12% decrease in total costs compared with traditional fuel vehicle fleets. Finally this study conducted a sensitivity analysis on the impact of gradually increasing the maximum load and charging rate of electric vehicles on various costs of the mixed fleet. Conclusion The analysis indicates that appropriately increasing the vehicle load and charging rate of electric vehicles can effectively reduce the operating costs of the fleet. The research results help logistics enterprises consider energy consumption costs and carbon emission costs and provide a theoretical basis for relevant logistics enterprises to develop reasonable transportation plans.