Through the unconfined compressive strength test, shrinkage test, X-ray diffraction(XRD)test, mercury injection porosimetry(MIP)test and scanning electron microscopy(SEM)test, the cement-modified expansive soil was systematically studied in the aspects of macroscopic mechanical properties, phase evolution and the micro-structure characteristics. The results show that cement addition can effectively improve the strength, swelling and shrinkage characteristics of expansive soil. After the cement addition, the microstructure of expansive soil changes significantly, and the gel phase hydration products of C-S-H during hydration reaction increase with the cement content. The soil particles can form a larger flocculent body and can benefit the pore distribution. The volume fraction of micro holes(diameter less than 100 nm)in modified expansive soil increases, indicating that the amount of hydration products is the key factor to soil strength, microscopic pore structure characteristics and shrinkage characteristics of cement-modified expansive soil.