The thaumasite sulfate attack（TSA） of water glass slag cement, ordinary Portland cement with 10%（by mass） of limetsone and the effects of fly ash and silica fume on TSA of water glass slag cement were studied. The erosion products after immersed in 5%（by mass） MgSO4 solutions for four years at 5℃ were analyzed by means of X ray diffraction（XRD） and Fourier transform infrared spectroscopy（FTIR). The pore structure of hardened paste of water glass slag cement was tested by mercury intrusion method. The results show that for ordinary Portland cement paste typical TSA occurs and water glass slag cement stone is suffered from slight sulfate attack caused by gypsum but not thaumasite and specimens with 10% silica fume, 20% and 40% fly ash are not attacked by sulfate. Water glass slag cement has excellent resistance to TSA due to its fine pore structure and its main hydration products are low alkali hydrous calcium silicate.