The elastic-plastic characteristics of the structure will lead to large dispersion of the residual displacements，which makes it difficult to predict the residual displacements accurately under strong earthquake excitations. In order to accurately evaluate and predict the residual displacements of the structure and realize the refined aseismic design，it is necessary to investigate the dispersion of the residual displacement of structures. In the light of this，based on a large number of classified ground motions，different normalized parameters are used to define the residual displacement ratio in this paper. The residual displacement ratios spectra of single degree of freedom（SDOF） systems are constructed by means of nonlinear response time-history analyses. The results are statistically organized to evaluate the influence of the following parameters: elastic-plastic characteristic parameters（ductility factor and strength reduction factor） and site condition. A simplified expression is presented to estimate the variation coefficient spectra of residual displacement ratios. It is concluded that the correlation between residual displacements and inelastic spectral displacements is better than that between residual displacements and elastic spectral displacements. The dispersion of the residual displacements is less affected by the site conditions. The variation coefficient spectra of residual displacement ratios increase with the increase of elastic-plastic characteristic parameters. It is suggested to select the inelastic spectral displacement as the normalized parameter，which can reduce the dispersion of the residual displacement ratios.