The silver-coated Al-Mg alloy powders were prepared by electroless plating using glucose and sodium potassium tartrate tetrahydrate as reducing agents. The main salt Tollens’ reagent were added into the reducing agent at different rates to get the composite powders with different microscopic morphologies. The results show that the alloy powders are coated best at the adding rates of 2~3 mL/min of the main salt Tollens’ reagent and have a satisfied electrical resistivity of 5.13×10-6 Ω·m. The analysis of microstructure and deposition process indicates that the reduced silver particles are first nucleation-deposited along alloy powder grain boundaries, and then act as catalytic nucleation centers to promote the silver reduction deposition. The coating grows up continuously, and finally a complete and homogeneous silver coating is formed on the surface of Al-Mg alloy powder.