Electroforming can realize high precision and complex shape parts manufacturing, making it widely used in the field of micromachining and micromanufacturing. The drawback lies in the nonuniform thickness distribution, which can cause quality issues including voids, pitting, and particles. In order to enhance the microstructure uniformity and electroforming performance, lanthanum chloride and cerium chloride were employed as additives in the copper electroforming experiment. This study analyzes the effects of lanthanum chloride and cerium chloride on the surface morphology, microhardness, tensile strength, and uniformity of electroformed copper deposits. The results show that adding rare earth elements into the electrolyte solution can improve thickness uniformity, promote ion mass transfer, and refine the copper deposit’s grain. Compared to the microstructure without adding additives, the copper deposit’s nonuniformity prepared with 1.0 g/L lanthanum chloride is 76.9% lower, and with cerium chloride, it is 72% lower. Additionally, the copper deposit prepared with lanthanum chloride exhibits superior overall quality compared to that prepared with cerium chloride.