Influences of aliphatic water reducer, polycarboxylic superplasticizer and aliphatic-polycarboxylic compound water reducer on cement hydration and the adaptability of these water reducers to cement were investigated by TOC, infrared spectroscopy, chemical analysis and mortar fluidity test.In addition, the technology and economy of three kinds of water reducers was compared.Experimental results indicate that the aliphatic-polycarboxylic compound water reducer could strengthen the dispersion property and accelerate the formation of calcium sulphoaluminate by establishing the collaborative mechanism of electrostatic repulsion and steric hinder, so as to improve the adaptability between cement and water reducer and the fluidity of mortar.The technology and economy of aliphatic-polycarboxylic compound water reducer is superior than the other two admixtures.