•The action mechanism of limestone powder includes four effects.•The physical effect of limestone powder depends on its particle size and amount.•The chemical effect of limestone powder relies on the alumina content. Limestone powder (LS) has been widely used in cement-based materials; and reportedly, can influence their properties by filler, nucleation, dilution and chemical effects. The action mechanism of LS mainly depends on its particle size and amount. The filler effect of LS refines the microstructure and reduces the porosity of cement-based materials. Its nucleation effect accelerates the hydration of C3S, increases the amount of hydration products and reduces the porosity of cement-based materials at early ages. Its dilution effect reduces the hydration peak of C3S, decreases the amount of hydration products and increases the porosity of cement-based materials. Its chemical effect promotes the appearance of third hydration peak, forms carboaluminate and reduces the porosity of cement-based materials.