Deposition of silicon film by a mercury-sensitized photo-CVD process has been simulated by numerical solution of governing equations with proper boundary conditions. The results indicate that the film deposition rate is controlled by homogeneous decomposition of the reactant, silane, in the gas phase. The growth rate increases but the film uniformity decreases with the increase of reactant inlet concentration. Increase in the reactant flow rate decreases the deposition rate but gives no effect on the film uniformity. Among process variables, the light intensity and the mercury-saturator temperature are important parameters.