A novel seismic robustness computational methodology is proposed for community building portfolio (CBP) coupled with lifeline networks based on probability‐cloud model. This method consists of three interrelated submodels, respectively, the building fragility analysis model of the main subsystem CPB, the water supply network (WSN) hydraulic simulation analysis model of the secondary subsystem WSN, and the probability‐cloud model. The proposed method can be used to predict the seismic robustness of hierarchical systems. The computational methodology uses a joint probabilistic model combined with building fragility analysis and WSN hydraulic simulation analysis to evaluate the robustness of CPB coupled with WSN. Due to the uncertainty in robustness analysis, a probabilistic‐cloud model procedure considering the uncertainty in seismic robustness is proposed. The procedure enables a qualitative and quantitative integrated analysis of the robustness of CBP coupled with WSN. Finally, a community with 1406 buildings in China is simulated to illustrate the method. The research outcomes can provide a useful reference for the seismic robustness analysis of CBP coupled with WSN.