Abstract: The shear strength characteristics of expansive soils and the relationship between their shear strength index and moisture content in Wuhan area are quantitatively analysed. The value table of c, and changing with the water content of weak and medium expansive soils in Wuhan area is worked out. A design method for deep foundation pits considering shear the characteristics of strength attenuation of expansive soils. It's proved by engineering practice that the proposed method is safer, more reliable and reasonable when moisture content is hard to be controlled and the expansion of the soils is relatively large.