Silver-coated copper (Ag-coated Cu) powder, combining the cost-effectiveness of copper with the oxidation resistance of silver, holds significant application value in photovoltaics and electronic pastes. In this study, Ag-coated Cu powder with a dense, uniform, smooth, and fully covered silver layer, as well as excellent dispersibility, was successfully prepared using the combined effects of ultrasonic and mechanical stirring. This study systematically analyzed the effects of different stirring conditions (mechanical stirring alone and mechanical stirring with ultrasonic oscillation), reaction rates (silver–ammonia solution supply rates of 1 mL/min to 9 mL/min), and silver contents (18%, 24%, and 28%) on the surface morphology and oxidation resistance of Ag-coated Cu powder. The results show that in the absence of ultrasonic oscillation, the uniformity and coverage of the silver layer were poor, with significant copper particle dissolution leading to hollow silver shells. Ultrasonic oscillation effectively reduced the roughness of the silver layer, improving its uniformity and coverage. Increasing the reaction rate had a minimal impact on the surface morphology but reduced the oxidation resistance of the powder. This study also analyzed the formation mechanisms of Ag-coated Cu with different surface morphologies, providing valuable guidance for producing high-quality Ag-coated Cu powder.