Abstract: It is easy to produce large cutting deformation during the cutting process of aluminum alloy 7075-T651 thin-walled parts, which affects the performance and service life of the products. Therefore, the influence of different tool geometric parameters on the cutting force of 7075-T651 aluminum alloy L thin-walled parts was investigated. The rake angle, clearance angle, and helix angle of the tool were selected as the main research variables, milling test of 7075-T651 aluminum alloy L thin-walled parts was conducted, and the effects of different tool geometric parameters on cutting force were analyzed. Through the analysis of the orthogonal test results, it is found that the tool helix angle has the most significant influence on the cutting force, followed by the rake angle, and then the clearance angle. The response surface model was fitted and solved by using the particle swarm optimization (PSO) algorithm combined with milling test data, and the milling cutting force prediction model of 7075-T651 aluminum alloy L thin-walled parts under different tool geometric parameters is obtained. The differential derivation of the established model shows that when the minimum cutting force is taken as the optimization goal, the corresponding optimization tool parameters are front angle 14.033°, clearance angle 8.212°, and helix angle 48.146°, with the cutting force of 159.71 N.