Abstract: Considering rock mass with discontinuous plane,based on unified strength theory,and introducing Lode parameter,unified strength parameters of materials are introduced,which are functions of Lode parameter and the intermediate principal shear stress parameter b.The strength criterion of rock mass with discontinuous plane,i.e.,failure criterion of considering the intermediate principal stress,is proposed,and the effective range of criterion is analyzed.The proposed criterion is verified by conventional triaxial experiment of diatomaceous soft rock.The changes of strength and unified strength parameters of rock mass with Lode parameter and parameter b are analyzed.Results show that unified strength parameters increase a certain value with increasing lode parameter,and then decrease with increasing lode parameter;and increase with increasing parameter b.