Abstract: A method of HLPC-CAD was proposed for the separation and analysis of the large monomers of polycarboxylate superplasticizer. The monomers belonged to the fatty alcohol polyoxyethylene ether. Agilent ZORBAX SB-C8 column was used as stationary phase and a mixture of methanol and water was used as mobile phase for gradient elution. Charged aerosol detector was used. Under optimum condition, the components of sample were separated successfully. The analysis results of HPLC-MS indicated that large monomers were separated according to the numbers of EO.