Silver-tin oxide powders were synthesized by the hydrothermal method with Ag(NH3)2+ solution and Na2SnO3 solution as raw materials and Na2SO3 as reductant. The precipitation conditions of Na2SnO3 solution and the reduction conditions of Ag(NH3)2+ were also investigated. The powders prepared were characterized by differential thermal analysis (DTA), X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and energy spectrum analysis. The results show that pH value of the solution is a key parameter in the formation of Sn(OH)4 precipitate and the reduction reaction of Ag(NH3)2+ can release H+ ions, which results in synchronous precipitation of Sn(OH)62- as Sn(OH)4. The reduction of Ag(NH3)2+ and precipitation of Na2SnO3 occur simultaneously and the coprecipitation of silver and tin oxide is reached by the hydrothermal method. The silver-tin oxide composite powders have mainly flake shape of about 0.3 μm in thickness and there exists homogeneous distribution of tin oxide and silver in the powder synthesized.