Abstract: Geometric nonlinearity is the essential problem of seismic analysis for civil engineering structures under strong earthquakes. In this paper, based on the numerical substructure method and the geometric nonlinearity theory of the plane Euler-Bernoulli beam-column element, nonlinear analyses for plane frame structures are equivalent to elastic analyses of linear elastic master structures, whose nonlinear properties are considered by two material and geometric nonlinear force correctors applied to the structures. At last, a seismic nonlinear analysis for a plane steel frame structure is performed to verify the accuracy and efficiency of the numerical substructure method considering the material and geometric nonlinearities; in addition, the geometric nonlinearity has a deep influence on the structural seismic response.