Abstract: Using light-burned magnesia prepared by calcining magnesite tailing to compensate the autogenous shrinkage of steam-cured cement paste was carried out. The fluidity and 3-day strength of cement mortars were measured to determine the suitable addition of magnesia. The hydration process of magnesia in paste was characterized by XRD and TG-DTA. And the pore structure of paste and microstructure of magnesia hydrates were analyzed by MIP and FESEM respectively. The results indicate that the hydration of magnesia is promoted rapidly in steam curing process, and slightly increases the porosity of paste. The continue hydration of magnesia in situ effectively compensates the autogenous shrinkage of paste after steam curing. The autogenous shrinkage of cement and fly ash cement paste with 4% magnesia is decreased by 33% and 17% respectively at the age of 14d.