Soluble dimethylsilane-diphenylsilane copolymer has been prepared by the reaction of a mixture of dimethyldichlorosilane and diphenyldichlorosilane with metallic sodium. The results show that the yield of copolymer increases when the ratio of these two monomers approaches unity，the molecular-weight decreases with the increasing of diphenyldichlorosilane content. The molecular-weight and composition of the copolymer are basically unrelated to the reaction time，but the yield increases with time at the beginning. Reaction temperature basically has no influence on the yield and molecular-weight of the copolymer. It also shows that the copolymer is amorphous.