Abstract: A novel and effective algorithm based on the member discrete element method (MDEM) is presented for dynamic analysis of space steel frames with semi-rigid joints, which incorporates nonlinear semi-rigidity of beam-to-column joints as well as material nonlinearity and geometric nonlinearity. The geometric nonlinearity is considered using rigid-body kinematics, while the inelasticity of material is modeled by introducing the defined plastic hinge model. Meanwhile, a virtual three-dimensional spring element with three translational degrees of freedom and three rotational degrees of freedom is proposed on the semi-rigid beam-column connection. The spring element quantifies the semi-rigidity of three-dimensional beam-column joints in a linearly distributed manner to the stiffness of the contact elements adjacent to these joints, and then the modified formula of the contact elements is derived through the energy equivalence principle. Additionally, the nonlinear cyclic behaviour of the beam-to-column connection is captured by the independent hardening model. The comparison between several sets of representative numerical results obtained by the proposed method and the published results verified the correctness and accuracy of the proposed method.