A hard coating silicon oxide film was deposited on flexible substrates by a PECVD system. Tertramethylsilane (TMS) and oxygen were employed as raw materials. Surface roughness and hardness of these films deposited under various TMS/O-2 gas flow ratio, rf power and chamber pressure were investigated. At adequate fabricated conditions, the original surface roughness of PMMA (similar to 3.36 nm) and PC (similar to 1.38 nm) substrates was markedly flatted to 1.52 and 0.39 nm, respectively. Meanwhile, the surface hardness of coated PMMA and PC substrates was also enhanced to 6.077 GPa and 3.978 GPa, respectively. The hardness of silicon oxide film deposited by TMS-PECVD system was superior to silicon oxide films prepared from e-beam evaporation and dipping technologies.