Low-heat portland cement (PLH) mortars and pastes with different dosage of fly ash and slag were prepared and the compressive strength and flexural strength of the mortars were tested.Phase composition of the pastes was tested by XRD while hydration heat flow was measured by calorimeter.The results show that the application of fly ash causes decreases in mortar strength and strength development rate.The influence of slag on mortar strength is not obvious.The phase composition of fly ash pastes is similar to that of the reference mixture.However,the content of CH is decreased by the use of fly ash.The application of slag can reduce CH content more significant than fly ash and meanwhile promote the formation of AFm.Both the heat flow and hydration heat of the PLH paste are decreased by fly ash and slag.The influence of fly ash on PLH hydration evolution is not significant whereas slag promotes the hydration evolution.