The effect of Na+ ion concentration on the crystalline phase composition and morphology of xonotlite crystals prepared in a CaO-SiO2-H2O system via hydrothermal synthesis was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that Na+ ion concentration has a significant impact on the composition and morphology of crystalline phases in the products under the initial conditions of a molar ratio of CaO/SiO2 of 1.0 and a reactant concentration of 0.05 mol·L 1 at 225°C for 15 h. The main crystalline phase in the products has a phase transition from xonotlite to pectolite, and the morphology changes from fibrous to broomlike shape with the Na + ion concentration increasing. Therefore, the content of Na2O in the raw material should be less than 5wt% for preparing pure xonotlite crystals via hydrothermal synthesis in a CaO-SiO2-H2O system. The effect of Na + ion concentration on the crystalline phase composition and morphology of xonotlite crystals prepared in a CaO-SiO2-H2O system via hydrothermal synthesis was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that Na + ion concentration has a significant impact on the composition and morphology of crystalline phases in the products under the initial conditions of a molar ratio of CaO / SiO2 of 1.0 and a reactant concentration of 0.05 mol·L 1 at 225 ° C for 15 h. The main crystalline phase in the products has a phase transition from xonotlite to pectolite, and the morphology changes from fibrous to broomlike shape with the Na + ion concentration increasing. Thus, the content of Na2O in the raw material should be less than 5% by weight for preparing pure xonotlite crystals via hydrothermal synthesis in a CaO-SiO2-H2O system.