Investigating the mechanism of early-strength polycarboxylate superplasticizer (ES-PCE) on cement hydration is helpful to the development, design and application of ES-PCE. In this paper, the influence mechanisms of ES-PCE and regular polycarboxylate superplasticizer (PCE) on early hydration of reference cement were analyzed by characterizing the hydration process, dissolution rate, hydration product growth, setting time and compressive strength of cement. The results show that both PCE and ES-PCE reduce the dissolution rate of cement suspension. The addition of PCE delays the induction and acceleration of cement hydration and reduces the heat release of hydration. ES-PCE only slightly delays the induction period of cement hydration, but shortens the acceleration period and hydration heat release is basically unchanged. Compared with reference cement, ES-PCE advances the initial setting time of cement by 10 min and the final setting time by 85 min. The incorporation of ES-PCE improves the early and late strength of cement. The 7 d compressive strength of cement with 0.2% ES-PCE (mass fraction) increases by 14% in comparison with reference group, while the strength of cement with PCE increases by only half of the former. The addition of PCE and ES-PCE releases the water in the granular flocculation structure of cement, which is beneficial to cement hydration, but their effects on hydration are opposite. A large number of carboxyl groups in the molecular structure of PCE complexes Ca2+ in the solution, inhibits the formation of crystal nuclei on the surface of cement particles, and plays a certain role of retarding coagulation. However, the carboxyl content of ES-PCE molecular structure is low, the complex effect of Ca2+ is weak, and the retarding effect is not obvious. When the effective water content in the system increases, the hydration of cement is promoted, which has the effect of early strength. In cement mortar with water cement ratio of 0.4, the mixing amount of ES-PCE is suitable to be controlled below 0.3%, which not only ensures the water reduction rate, but also enhances the early and late strength of cement.