The invention provides a superplasticizer for facilitating cement hydration. The superplasticizer is prepared by free radical copolymerization reaction of a monomer a, a monomer b, a monomer c and a modified monomer d, wherein the modified monomer d is prepared by a reaction of a monomer d and nanometer SiO2; the viscosity average molecular weight of the superplasticizer is controlled to be in a range from 30,000 to 80,000. The invention further provides a preparation method of the superplasticizer and application of the superplasticizer in promotion of the cement hydration. The preparation process of the superplasticizer is simple, the use is convenient, and the cost is low; the superplasticizer is prepared by importing superlong side chain polyester, zwitter ions and nanometer particles and can remarkably facilitate early-stage hydration of cement, so that the compressive strength of concrete is improved; furthermore, at room temperature or low temperature, the early-stage reinforcement effect is greatly remarkable, and the middle-stage and later-stage strength is stably improved; besides, the superplasticizer has stronger adaptability for materials, and is suitable for low-temperature large-mixing-amount mineral admixture concrete and prefabricated part concrete.