A model that combines mass transportation process and surface kinetics is firstly applied to analyze the GexSi1-xCVD process. The temperature

velocity ad concentration distributions in the reactor are calculated by the partial different equations of fluid dynamics. The surface kinetics is used to discuss the deposition of Si and the mass transportation process is used to discuss the deposition of Ge. The theoretical relationship between the initial conditions and the Ge composition x in the solid has been established. The calculated result of the growth rate and the Ge composition in the solid agree with the experiment data. The increase of the growth rate and Ge composition x with the increase of initial GeH4 concentration is explained quantitatively by our model.