Abstract: This is an article in the field of ceramics and composites. The mix proportion of limestone powder cement is designed based on the mixture design principle, and the effects of limestone powder content and particle size on the mechanical properties of limestone powder Portland cement system are studied. The hydrate phase and microporous structure of portland cement paste mixed with 0.44 mm and 0.025 mm limestone powder were analyzed by X-ray diffraction (XRD) and low field nuclear magnetic resonance (NMR). The results show that the two limestone powders have a negative effect on the early compressive strength. However, with the progress of hydration, limestone powder within a certain dosage range can enhance the later strength of cement. When the dosage exceeds this range, the compressive strength decreases gradually with the increase of dosage. Although the addition of limestone powder produces hydrated calcium carboaluminate in the hydration products which is conducive to the mechanical properties of cement stone, its coarsening of microporous structure greatly reduces the compressive strength of limestone powder cement specimens when the content of limestone powder exceeds a certain value.