The UV spectroscopy of dimethylsilane-Diphenylsilane Copolymer has been investigated，and its molecular weight has been related to λ_max and ε max. It has also been found that there is an absorption occuring at 325nm，when the concentration of the copolymer is higher than 0.03g/1 approxiately. The absorbance is related to molecular weight and concentration of the copolymer，while the position is unchanged.