The effects of gas flow, temperature and concentration on the growth process of silicon epitaxial film in a horizontal single-wafer reactor of trichlorosilane (SiHCl3) were examined by 3-dimensional numerical simulation. For uniform growth over the silicon wafer, it is effective to grow the film on rotating susceptor under high SiHCl3 concentration with a high gas velocity in a reactor of low height. However, in cases of comparatively low gas velocities and low SiHCl3 concentration, uniform growth of silicon can be achieved by dividing the reactor inlet into three sections and by regulating each inlet width and gas velocity to obtain optimum conditions, and thereby of controlling the starting position and strength of buoyancy convection. Near the center of the wafer, a uniform growth rate cannot be archived by rotation of the susceptor, so a decrease in the gas velocity at the center of the reactor should be avoided.