In order to study the effect of limestone powder fineness and dosage on the rheological properties and hydration process of cement pastethe rheological properties of freshly mixed paste were tested by Anton Paar rheometerand the thixotropy of paste was characterized by calculating the thixotropic annulus area. Meanwhilethe mechanism of the influence of limestone powder on the rheological behavior of cement paste was explained by using the results of wet stacking density test and the calculation of the thickness of water film powder on the rheological behavior of cement paste was clarified by microcalorimetry test and quantitative analysis. Finallythe influence of limestone powder on the hydration process of cement was clarified by microcalorimetric test and XRD quantitative analysis. The results show thatat 10% dosagethe doping of 1 000 mesh (525 μm) stone powder reduces the yield stress by 48.4% compared with that of 400 mesh (1734 μm) stone powderbut it improves by 15.6% compared with that of 600 mesh stone powder. At the same finenessthe doping of 10% and 20% 600 mesh (1123 μm) stone powder reduces the yield stress of the paste by 76.7% and 81.8% compared with that of the blank grouprespectively. Doping stone powder reduces the thixotropic behavior of paste and changes the variation rule of thixotropy with time. Increasing the fineness and dosage of stone powder increases the wet packing density of pasteand the thickness of water film layerresulting in a decrease in yield stress and consistency of slurry. Increasing the fineness of stone powder can shorten the hydration induction periodmove the second exothermic peak of hydration forwardand promote the early dissolution of C3S and the generation of C-S-Hwhich can accelerate the hydration process of cement.