The effects of adding cosolvents of diglyme and 15 crown 5 to the reaction mixture of Wurtz type coupling of dichlorosilanes on the yield and relative molecular mass dispersity of polymethylphenethylsilane(PMPES) were discussed. The results show that addition of 10% (volume ratio of diglyme to toluene) diglyme as a cosolvent to the reaction mixture leads to the yield increase of PMPES with a monomodal distribution of relative molecular masses. Adding 10% diglyme to the reaction mixtures, the yields of polymethylcyclohexylsilane(PMCS) and copolymers (polymethylphenethylsilane co methylcyclohexylsilane), (the molar ratios of methylphenethyldichlorosilane to methylcyclohexyldichlorosilane were 2.0, 1.0 and 0.5, and the copolymers were abbreviated by Copolymers Ⅰ, Ⅱ, Ⅲ, respectively) are 47%, 52%, 54%, 53%, respectively. Their relative molecular masses ( w ) almost reach 10 5. These polysilanes were characterized by 1H NMR, IR and UV absorption spectrum. The effects of adding cosolvents of diglyme and 15 crown 5 to the reaction mixture of Wurtz type coupling of dichlorosilanes on the yield and relative molecular mass dispersity of polymethylphenethylsilane (PMPES) were discussed. The results show that addition of 10% (volume ratio of diglyme to toluene) diglyme as a cosolvent to the yield increase leads of the yield of PMPES with a monomodal distribution of relative molecular masses. The addition of 10% diglyme to the reaction mixtures, the yield of polymethylcyclohexylsilane (PMCS) and copolymers (polymethylphenethylsilane co methylcyclohexylsilane) , the the molar ratios of methylphenethyldichlorosilane to methylcyclohexyldichlorosilane were 2.0, 1.0 and 0.5, and the copolymers were abbreviated by Copolymers I, II, III, respectively) were 47%, 52%, 54%, 53%, respectively. (w) almost reach 10 5. These polysilanes were characterized by 1H NMR, IR and UV absorption spectra.