To compare with ordinary Portland cement mortars, the resistance to the sulfate attack of the limestone slag cement with different content of limestone powder which was immersed in 3%(by mass) Na2SO4 solution for a long period was investigated. The results show that the limestone slag cement has better long term strength and sulfate resistance; after being immersed in Na2SO4 solution for 360d and 730d, the sulfate resistance coefficient（SRC） of the limestone slag cement mortars containing 60%, 50%, 40% of limestone powder in test specimens reach 1.10，1.08，1.18 for 360d and 1.06，1.10，1.11 for 730d respectively. That is higher than the ordinary Portland cement mortars up to 42.9% and 55.9%. To compare the compressive strength of the limestone slag cement with that of ordinary Portland cement at the standard curing 28d, the compressive strength of the limestone slag cement can be increased by 36.9%,43.7%,48.3% and 40.2%，55.3%，57.7%, but the compressive strength of ordinary Portland cement can be decreased by 5.2% and 30.3%.