Abstract: A numerical simulation method was employed to carry out an in-depth study on the complex molten pool flow behavior and the formation and inhibition mechanisms of porosity in the laser welding process of copper terminals. A coupled heat transfer–flow model of laser scanning welding was established, and the effect of scanning trajectory on depth of fusion and joint area was explored. The generation and inhibition mechanisms of joint porosity were clarified, and the mechanical peeling force at the joint based on the response surface method was predicted, with the welding parameters optimized. The results show that the laser beam energy can be transmitted more stably in the keyhole wall and the bottom of the keyhole under the elliptical line trajectory, resulting in a larger average depth of fusion of the weld and joint area. The depth of the keyhole and the temperature gradient are the main factors affecting the generation of porosity, and the volume of the porosity of the weld under the elliptical line trajectory is small. The generation position is shifted with respect to the position of the weld so that the porosity has little effect on the performance of the joint. After the optimization of welding parameters for elliptical line trajectory, the laser beam energy is transferred to the bottom of the keyhole, which makes the average depth of fusion of the weld and joint area larger. The optimized welding parameters yield an elliptical line trajectory, laser power of 4 224 W, scanning amplitude of 2.5 mm, ratio of 3:1, number of scanning circles of 3, and mechanical peeling force at the joint of 779.6 N, which is 1.26 times higher than that of fixed-point welding.