We perform a numerical simulation of the gas flow pattern, and the temperature and concentration distributions in a horizontal cold wall atmospheric CVD reactor with an adjustable tilt angle of the susceptor. The effects of mixed convection on heat and species transport are also examined in the range 2 < Re < 10 and 600 K < susceptor temperature < 1200 K. We find when the inertia force is maintained constant, the transverse rolls increase the vertical temperature gradient and decrease the vertical mass fraction gradient above the horizontal susceptor. On the other hand, the tilt angle arrangement enlarges the concentration gradient along the trailing edge of the susceptor. Consequently, the uniformity of growth rate is increased. The effects on the flow fields due to the tilt angle configuration and various thermal boundary conditions of the susceptor are also explored.