In this paper

the transport process of the gas reactants for growth of

Ⅲ-Ⅴ compounds in MOCVD system has been analyzed.It is given that the mass quantity entered into the reactor of the MOCVD dependes on the structure of the MOCVD and on thecharacter of the reactants.As a result

the transport of the gas reactants in MOCVD systerm is determind not only by the carry of the carry gas but also by the concentration diffusion of the reactants.So that

the mass quantity of the reactants entered into the reactor of the MOCVD is much more than the data calculated in term of carry principle.Accoding to the theory analysis

the calculated formula has been obtained.It gives the dependence of the transported mass quantity of the reactants on the structure ofMOCVD

on the flowes and diffusion coeficient of the gas.Using this formula

some experimental phenomina can be expiated:why the Ⅴ/Ⅲ ratio grwon

Ⅲ-Ⅴ compouds has to be higher than the chemical component of the materials

why the Ⅴ/Ⅲ ratio reported by different papers were different data and why the different apparture used different Ⅴ/Ⅲ ratio to grow same materials.