This paper is based on the mechanism of UV photodecomposition of polysilane，utilizing the sflane free radical generated from the photodecomposition to initiate the polymerization of monomer styrene．Studies of the influences of initiating time，concentration of polysilane，and UV characteristic absorption wavelength (λmax) of polysilane on the percentage of olymerized conversion，show that polysilane can be characterized as photoinitiator．The percentage of conversion increases with the square root of the concentration of polysilane．The closer the λmax is to the wavelength of source light，the more effective the polymerization is．