Expansive soil is called as “problem soil”, which has a characteristic of swelling by absorbing water and shrinking by losing water. So buildings and sub-grade which are built on expansive soil, are easier to damage for lager deformation. Due to the large-scale urban construction, ground surface was covered in a wide range. For example, in tropics and subtropics areas, the water transfer in the expansive soil is influenced by the gradient of temperature, which is different between the central area under the road surface and road-side bare area. Because of the hysteresis of water transfer, the water content distributing is not uniform, which lead to the different swell-shrink performance in different zone, herewith will change some parameters of the expansive soil and finally affect its stress field and the displacement field. Take the road as the example: The road is a strip belt-shaped coverage. Both in dry and wet season, the thermodynamic field and water-flowing field is uneven between the central area under the road surface and road-side bare area, so the displacement field and the stress field on the cross-section under the road is uneven. Under the load of vehicle, the non-uniformity stress distributing in the soil is further aggravated, and the same to the displacement in the underlying sub-grade, which is a significant factor in aggravating the dehiscence of road surface. Comparing to general soil, expansive soil has a completely different distribution of temperate field and water-flowing condition because of its swell-shrink characteristic. By studying on the relationship between the thermodynamic field and the stress-strain in the expansive soil, it can find out how the climate affect the engineering expansive soil, and provide the theory basis for improving expansive soil.