Abstract: With polycondensates of methyltrimethoxysilane（MTMS） as coating materials，silica sol modified by 3-(methacryloxypropyl)-trimethoxysilane (MEMO) as inorganic strengthening materials，the transparent silica sol modified methylsilicone film was prepared on polycarbonate (PC) by the sol-gel method. The properties of the coating solution and film with and without MEMO were studied. The film thickness was calculated by the envelope method and compared with SEM results. The results showed that the addition of MEMO could extend gelation time and improve stability of the coating solution and form thicker crack-free film with ease. The film improveed the transparency of PC. The addition of MEMO had no effect on reflection-reducing property and hardness. The film thickness increased with ageing time. The thickness calculated theoretically was close to that measured by SEM.