For estimating the response spectrum of offshore engineering structures with different damping ratios, the damping modification factor (D_MF) model of offshore engineering response spectrum was studied. Based on 5 680 horizontal offshore ground motion records from S-net network, we analyzed the effects of source parameters such as moment magnitude, fault depth, and earthquake type, as well as source distance and sediment thickness on D_MF, and proposed a D_MF model for horizontal acceleration spectrum from offshore ground motions considering damping ratio and spectral period, which was compared with onshore models. Results show that moment magnitude and source distance had significant impact on D_MF. D_MF with low damping ratios increased with the increase in moment magnitude and source distance, while D_MF with high damping ratios decreased with the increase in moment magnitude and source distance, and D_MF was not sensitive to the influence of fault depth and sediment thickness. Compared with the study of onshore area, the D_MF values of shallow crustal and upper-matle earthquakes in this study were slightly larger under low damping ratios and medium-long periods. When spectral periods were greater than 0.1 s or less than 0.1 s, the influence of damping ratio on D_MF could be simulated by cubic or quadratic logarithmic polynomials, and the influence of spectral period could be expressed by quartic or cubic polynomials. There were significant differences between offshore D_MF model and onshore models. The D_MF model for response spectrum from offshore ground motions proposed in this paper provides reference for the determination of seismic design spectrum of offshore engineering under various damping ratios.