The CaO-Na2CO3 activated slag (CNS) mortar and the ordinary Portland cement (OPC) mortar were immersed in sodium sulfate and magnesium sulfate solution respectively, and the flexural strength, compressive strength and SO2-4 concentration in different depths of CNS and OPC mortars were studied before and after sulfate corrosion. Meanwhile, the corrosion products and pore structure of CNS and OPC mortars were analyzed by XRD, SEM and MIP. Then the corrosion mechanism of sodium sulfate and magnesium sulfate on CNS and OPC mortars was compared and discussed. The results show that the hydration products of CNS mortar are mainly calcium aluminium silicate hydrate (C-A-S-H) with low Ca/Si ratio, and there is no calcium hydroxide. The pore structure of CNS mortar is better than OPC mortar due to the filling effect of calcium carbonate, and the sulfate resistance of CNS mortar is greater than that of OPC under the same corrosion environment. The corrosion products of CNS mortar under magnesium sulfate are mainly brucite (the mortar on the specimen surface will be peeled off together in the later stage of corrosion) and non-adhesive magnesium aluminium silicate hydrate (M-A-S-H). Compared with sodium sulfate, magnesium sulfate is more corrosive to CNS mortar.