The temperature variation and salt expansion characteristics of natural sub-chlorine saline soil in Lop Nur under cyclic freezing and thawing are investigated. Test results show that under the action of cyclic freezing and thawing, the temperature fluctuation in a same soil layer keeps consistent; temperature distributes in a parabolic shape as freezing and thawing cycle proceeds, with the first and the second layers near the cold end surface undergoing great temperature changes while the third layer to the fifth layer experiencing small temperature change. Sub-chlorine saline soil with low liquid limit silt has a good effect of salt expansion and accumulation; the salt expansion increases as temperature declines, and vice versa, with the maximum salt expansion reaching 7.61 mm. In the first four periods (cycles), the salt heaving effect is obvious, and the salt expansion amount is about 80% of the total salt expansion. Salt expansion in the first six freeze-thaw cycles increases gradually, but the trend slowly attenuates, and tends to be stable in the seventh freeze-thaw cycles.