Carbon/carbon(C/C)composite are important materials for aeronautical and aerospace industries because of their low density and swell factor,high specific modulus,excellent environmental stability,and anti-frictional and anti-thermal shock properties.However,the performances C/C composite depend on the structures and morphologies of the materials which are direct results the chemical vapor infiltration(CVI)process[1].In this work,the chemical reaction mechanism especially the formation and transport of active centers of model molecules is studied using density functional theory combined with transition state theory and Rice-Ramsperger-Kassel-Marcus theory [2].