Abstract: The expansive soil in the Nanyang section of the South-to-North Water Diversion Project is situated at the seasonal frozen soil region, which is easy to be affected by the freeze-thaw cycles. The freeze-thaw cycles will also change the structures of the expansive soil and affect its physical and mechanical properties, which will make a notable impact on the construction of the works. In order to study the factors and interactions on the physical and mechanical properties of the expansive soil, the Nanyang expansive soil was taken as a case study. The deformation measurements and unconfined compressive tests were carried out for understanding the physical and mechanical properties of the Nanyang expansive soil samples under the conditions of different water contents, freezing temperatures and freeze-thaw cycles. The testing results show that the water content has a great influence on the mechanical properties of the expansive soil: the higher the water content, the greater the strength and elastic modulus decline. The freezing temperature has a great influence on the volume change, especially -10 ℃. Some studies of the significant influence of the water content, freezing temperature, the number of freeze-thaw cycles as well as the interaction between different factors on the physical and mechanical properties of the expansive soil were made on the basis of the theory of significance analysis. The study results show that the impact of the water content on the mechanical properties of the expansive soil is the most remarkable, and the interaction between the freeze temperature and water content has a significant impact on the unconfined compressive strength. And the freezing temperature is the most significant influence on the volume change, and the interaction between the water content and freezing-thaw cycles has a certain influence on the volume change. Therefore, we should not only consider the influences of a single factor, but also consider the interactions of various factors in studying the physical and mechanical properties of the expansive soil under the conditions of the freeze-thaw cycles.