Abstract: Expensive soil is a kind of special clay, with engineering features of hydro-expansiveness, disintegration, softening, shrinkage after losing water, drying crack and hardening. When the expensive soil is blended with cement, its engineering features will be improved. The expansive soil of Nanyang section of the Mid-route of South-to-North Water Transfer Project is selected to perform the test of cement-modification in this paper. The optimum blending quantity of cement is determined by free  expansion rate test after the improvement. And the improving effect of reducing swelling potential by cement-modification is studied by tests of expansion and shrinkage. Meanwhile, the reinforcing effect of cement-modification on the suppression of module and strength softening of expansive soil is researched by unconfined compression test and compression test. A scientific and valuable basis is provided for the design and construction of site cement-modification of expansive soil.