Abstract: The determination of shear strength of expansive soil is always an important research topic due to its fissuring and over-consolidation property. The shear strength is of much significance in the design of slope in the expansive soil area. Using the expansive soil in Nanyang Area, Henan Province as an example this paper discusses in-situ shear strength test method including specimen preparation. The improved formulas for estimation of shear strength of the expansive soil are also presented. The results of landslides stability analysis indicate that the method suggested is rationale.