Abstract: During the seismic process of earthquakes, larger-scale civil engineering structures might fail due to the serious damage to some key structural members, whereas most structural components might remain elastic and experience small deformation. It is a challenging task to simulate the behavior of such structural systems due to the trade-off between computational efficiency and numerical accuracy. This paper presents an efficient and practical elastoplastic numerical substructure method, in which the whole structural seismic analysis is divided into linear elastic analysis of a master structure and nonlinear analysis of limited numbers of small-scale substructures, to balance the computational efficiency and numerical accuracy. During the linear elastic analysis of the master structure, the formation and LU triangular decomposition need to be done only once as the equivalent stiffness matrix remains constant, resulting in high computational efficiency of the master structure. Rational or refined models can be used in substructure systems to model the local damage mechanism, improving the numerical accuracy of the whole structure. Seismic analysis of a reinforced concrete frame structure is performed to verify the novel numerical substructure method.