In order to study the influences of limestone powder parameters on the hydration heat of cement, the effects of different content and particle size of limestone powder on the hydration heat and hydration heat rate of cement were analyzed by TAM Air-eight-channel microcalorimeter. The results show that with the increase of content of limestone powder, the hydration heat and hydration heat rate of auxiliary cementitious materials generally show a trend of decreasing. The hydration heat and hydration peak rate of 15% (mass fraction) limestone decrease the most, the hydration heat at 400 mesh is 223.22 J/g, the hydration peak rate is 2.399 2 mW/g, the hydration heat at 3 000 mesh is 215.98 J/g, and the hydration peak rate is 2.214 0 mW/g. Meanwhile, when the content of limestone powder is large, the influence of particle size on the hydration reaction is more obvious. Too small or too large particle size will increase the hydration heat and hydration heat rate. When the particle size of limestone powder is 1 250 mesh, the hydration heat is small and the hydration heat rate is low. Through phase analysis, it is found that the system with limestone powder do not produce new substances. When the content of limestone powder is 15% (mass fraction) and the particle size is 1 250 mesh, the diffraction peak intensity of Ca(OH)2 is the highest and accompanied by the formation of a large amount of C-S-H, indicating that this group of limestone powder can greatly promote the hydration reaction of cement.