The polymeric admixture, the sodium-carboxymethylcellulose (CMC) /poly sodium p-styrene sulfonate (PSS) / poly vinyl acetate (PVAc) was synthesized and applied in cement mortars. The polymer was tested by FTIR and SEM, and the results indicate that the ideal molecular structure is synthesized. The effect of addition amount of polymeric admixture and water-to-cement ratio on mechanical properties of cement mortars was studied. The polymer-modified mortars under the optimum water cement ratio and optimum polymer cement ratio, the flexural strength of polymer-modified mortars are 1.45, 1.21, and 1.17 times higher than the plain cement mortar at age of 3, 7, and 28 d, respectively. The compressive strength of polymer-modified mortars at age of 3, 7, and 28 d are 1.55, 1.40, and 1.2941 times higher than that of the plain cement mortar, respectively. Scanning electron microscope (SEM), FTIR and TG were used to analyze the effect of polymer emulsion on cement hydration reaction. The results show that the polymer emulsion can promote the hydration reaction of cement.