Abstract: In this paper the uniformity within and among the wafers in LPCVD reactors is analyzed by means of mathematical models, which describe the diffusion-reaction process between two adjacent wafers and mass, heat transport in the annular flow region. Results indicate that the uniformity h and effectiveness factorη within each wafer can be represented as function of volume change modulus ε and diffusion modulus φ; approprately installing heating device out of reactor tube can improve the uniformity from wafer to wafer or increase the conversion of reactant, These conclusions can serve as guidance tor design of LPCVD reactors and selection of operation parameters.