Abstract: Considering the variation of volume of soils,the analytical expressions for distribution of the stress and displacement in unsaturated soils after the expansion of spheric cavity could be deduced on the basis of the cavity expansion theory combining with the Modified Cambridge Model.Then,the effect of the over-consolidation ratio on the results was analyzed.The theoretic instructions for some geotechnical engineering problems in unsaturated soil areas could be provided,such as the penetration of piles,cone penetration tests,etc.