Abstract: This paper deals with the expressions of the yield criteria for perfect plastic rock-soil in stress space and strain space, and the characteristics of the yield curves on a meridian plane and a π plane. In this paper, a unified formula is used to represent the ten yield criteria which are widely adopted at present, and a unified expression of the strain yield criterions is also derived through transformation. And moreover, different derevative values of the stress yield functions and the strain yield functions are given to obtain the elasto-plastic matrix of the perfect plastic rock-soil, and all the results can be used for practical purposes.