Abstract: The mechanical behaviours of rock mass of major civil engineering are dramatically affected by the presence of joints, and the major discontinues can cause a variety of problems in both surface and underground constructions. Realistic simulation of the mechanical behaviours of rock joints becomes an important part of modelling the rock mass. A three-dimensional joint element based on the framework of elastoplastic constitutive model is proposed to account for dilatancy, roughness and undulating surface of discontinuities. To simulate the behaviours of joints under complex loading condition, dilatancy and reduction zone are suggested. An integration algorithm of constitutive equations based on the Euler backward integral method is used, and the consistent tangential matrices are derived. An ABAQUS user-defined element subroutine using this model is programmed, three experiments of direct shear tests, cyclic shear tests and restricted normal stiffness shear tests are simulated by ABAQUS, and the calculated results are analyzed to verify this method.