Abstract: Expansive soil is a kind of poor engineering geology soil because it has the property of water expansion and water shrinkage. In this paper,cement,steel slag powder and NaOH are used to improve the expansive soil and carry out the freeze-thaw cycle test. Then,the physical and mechanical properties of the improved expansive soil and the unmodified expansive soil after different freeze-thaw cycles are tested,such as volume,free expansion rate and unconfined compressive strength. At the same time,the micro electron microscope scanning analysis is carried out,in order to study the change rule of physical and mechanical properties of expansive soil improved by steel slag cement under the action of freeze-thaw cycle. The test results show that: Under the action of freeze-thaw cycle,the volume change rate of improved expansive soil is significantly lower than that of unmodified expansive soil. With the increase of curing age,the volume expansion of the improved expansive soil becomes smaller under the action of freeze-thaw cycles. With the increase of freeze-thaw cycles,the volume change rate tends to be stable,and the free expansion rate decreases with the increase of freeze-thaw cycles. Under the action of freeze-thaw cycle,the no-load expansion rate of ES-SSP-C sample is low. Under the action of freeze-thaw cycle,the improved expansive soil has better anti expansion performance than the unmodified expansive soil,and the effect of steel slag powder cement modified expansive soil(ES-SSP-C-SH)with NaOH active activator is the most obvious.