The characteristics of CoMoP impregnation solution,dried and calcined samples of CoMoP impregnated with γ-Al2O3 were investigated by Raman spectroscopy.Effects of phosphorous content on the structures of the active phases in CoMoP impregnation solution during the impregnation process were studied.The results indicate that the active phases in CoMoP impregnation solution with lower phosphorous content are composed of several heteropoly compounds,such as CoxH6-2x［P2Mo5O23］,CoxH7-2x［PMo11O39］or CoxH3-2x［PMo9O31］and CoxH3-2x［PMo12O40］.CoxH6-2x［P2Mo5O23］is dominant in CoMoP impregnation solution when phosphorous content increases.When the impregnation solution is impregnated into the cavities of γ-Al2O3,higher phosphorous content prevents CoxH6-2x［P2Mo5O23］ from converting to seven poly-molybdate.The presence of tetrahedral and octahedral Mo species is attributed to the interaction between Mo and P in the active phases.