Abstract: X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to observe the compound change law of geopolymer reaction and the hydration reaction of calcium silicate by adjusting the molar ratio of SiO₂/Al₂O₃, CaO/Al₂O₃ and Na₂O/Al₂O₃ in the geopolymer. Then the compound synergistic effect of geopolymer reaction and the hydration reaction of CaSiO₃ was explored. Furthermore, the formation mechanism of early strength in geopolymer was revealed. The results show that the geopolymer reaction products contain a certain amount of quartz component. The physical properties and chemical properties of quartz are very stable and the quartz strength is high. The products of hydration reaction of CaSiO₃ are mainly CaSiO₃ hydrate whose internal structure is loose. With the mole ratios of SiO₂/Al₂O₃ and CaO/Al₂O₃ increasing, the degree of geopolymer reaction increases first and then decreases, and the degree of hydration reaction of CaSiO₃ increases first and then stabilizes and is greater than the degree of geological polymer reaction. When the SiO₂/Al₂O₃ molar ratio is 3.8 and the CaO/Al₂O₃ molar ratio is 2.750, the compound synergistic effect of geopolymer reaction and hydration reaction of CaSiO₃ is the best. At this time, the proportion of quartz in geopolymer is about 66wt%, the proportion of CaSiO₃ hydrate in geopolymer is about 24wt% and the mechanical properties are good.