In this paper, on the base of idealizing the asperities of discontinuity by statistical methods, the yield rule of discontinuity is considered as more practical nonlinear model from the other way(which is different from refcrence[1]. and set up the physical equatation by using the physical meanings of the model. Then the obvious equatations of yield rule and clilatancy of discontinuity is given, in order to evaluate the practical shear strength of discontinuity. In addition, the destroy state of discontinuity during shearing is described