The water stability of lime-treated expansive soil is researched through compaction test, unconfined compression test and compression modulus test on weak expansive soil and lime-treated expansive soil in association with the test results of soil-water characteristic curve (SWCC) by other scholars. Results reveal that the compaction scope of lime-treated expansive soil is wider than that of natural expansive soil, and the optimum water content and the maximum dry density respectively increases and decreases linearly with the increment of lime content. The reduction of unconfined compressive strength and compression modulus of lime-treated expansive soil is the largest after one-day water absorption, and with the increase of water absorption time, the reduction rate gradually gets smaller and finally tends to be stable. Moreover, the reduction of unconfined compressive strength is up to maximum after 1 day’s wetting-drying cycle, and with the increasing of wetting-drying cycle, the reduction rate also decreases. The decreased margins of unconfined compressive strength and compression modulus of lime-treated expansive soil are remarkably smaller than that of natural expansive soil, indicating that the water stability of lime-treated expansive soil is greatly improved. In addition, researches of SWCC also show that the water stability of lime-treated expansive soil is improved.