The influence of polymer coating on the shrinkage of cement-based materials is comparatively analyzed in this paper. First of all, the relationship between cement-based materials shrinkage and water loss is discussed. Furthermore, some surface topography differences and pore structure changes of cement-based materials causing by polymer coating are investigated. At last, the affecting mechanism of polymer coating on reducing cement-based materials shrinkage is investigated. The results show that polymer coating can significantly reduce the shrinkage of cement-based materials. A more thick coating gets a higher shrinkage reducing ratio. There is a close relationship between cement-based materials water loss ratio and shrinkage ratio. Polymer coating can make the micro-crack on cement-based materials surface disappear. The cement-based materials coated with polymer have a lower surface layer cumulative average porosity than blank control group. The evaporation of capillary water and the development of negative capillary pressure in cement-based materials are controlled by polymer coating, thus the shrinkage becomes small.