Abstract: ln this paper is prensented a stress-dropping strain-softening model based on strain-softening be-haviour of geomaterials,Calculation of dropping-stress and epuilibrium condition of damage surface are discussed.Formulas calculating stress and displacement fields of expansion of cylindrical cavity are derived with this model.The effect caused by different strain-softening rates on stress and displacement fields,development of the plasticzone of expansion of cylindrical cavity is analyzed.