Abstract: It’s shown by experiments that the classic plastic mechanics is difficult to reflect the real deformation mechanism of geomaterials.The reason is that the classic plastic mechanics is based on the hypothesis of the traditional potential theory,the hypothesis of the associated flow rule and the hypothesis of not considering rotation of principal stress.The generalized plastic mechahics gives up all these hypotheses and gets all its plastic formulas from solid mechanics directly,so it can be used for both geomaterials and metals.