Abstract: The volume change law of cement hydration process was quantitatively studied by density measurement, and the hydration process of paste test blocks with different water-cement ratios was quantitatively measured with the change of age density. The relationship between volume change and cement hydration process was discussed. X-ray diffraction method was used to confirm the change of each phase in the hydration process to verify the reliability of the density measurement analysis method, and the relationship curve between specific volume and compressive strength was obtained. The results show that this method could be used to quantitatively characterize the volume (or specific volume) change of hydration process, which had a good quantitative relationship with its compressive strength, and the change of compressive strength could be predicted by specific volume measurement. A new test method was provided to characterize the characteristics of cement hydration process.