Cement mortars were prepared and immersed in Na2SO4solution with different pH values, i.e. 5, 9, and 13, up to 330days. The contents of leached Ca2+ and OH- in solution were analyzed through chemical titration, and products of cement mortars during attack were analyzed by X ray diffraction and differential scanning calorimetry. In addition, scanning electron microscope was further applied to investigate nCa/nSi and microstructures. The results show that the content and rate of calcium leaching in high pH environment are larger than that in the lower pH solution. The leached Ca2+ will continue to react with the diffused SO2-4 to form more CaSO4·2H2O at the lower pH environment. The formation of gypsum in low pH value is accompanied with the consumption of calcium hydroxide, which can cause the decalcification of C S H gel and decrease the gelling property of cement mortar, and result in softening and spalling of the specimens.