In this article, micro investigation of the cement stone under sulfate erosion is carried out by using SEM (Scanning Electron Microscope). The XRD method is also employed to semi-quantitatively analyze the erosion product. The cement stones whose water-cement is 0.45, 0.55, 0.65, respectively, immersed in sulfate solution whose sulfate ion concentrations is 0%, 3%, 4%, 5%, 6%. After different immersion time of 24 days, 45 days and 60 days, the microstructure of samples is detect by the SEM. The energy-dispersive X-ray analysis (EDX) is taken to determine the general elements in samples. The XRD method is employed to semi-quantitatively determine the weight percents of ettringite and gypsum in cement stone samples. Through comparative analysis, it tries to point out how the sulfate ion and water-cement ratio will affect the erosion products.