In order to address the difficulty to quantifying the emergency coordination ability of related organizations during the formation of urban flood emergency plans，a method to evaluate the robustness of inter-organizational networks for urban flood emergency response considering cascading failure was proposed. First，the inter-organizational networks for flood control emergency plans in Beijing，Shanghai and Shenzhen were established，and attack strategies and evaluation indexes of network robustness were proposed. Secondly，network characteristic statistical parameters are computed，and the network topology properties were analyzed. Then，the natural connectivity was selected as the robustness indicator to evaluate the network robustness under node single-attack strategy and continuous attack strategy. Finally，the robustness of networks under different attacks was compared，and the key organizations that have a great influence on robustness were found. The results indicate that inter-organizational networks of urban flood control emergency plans in Beijing，Shanghai，and Shenzhen have small-world and scale-free characteristics. Under single attacks of nodes，compared with the case of non-cascading failures，the robustness of inter-organizational networks is weaker considering cascading failures. Organizations with a large number of failure nodes are key to making the networks robust. Under continuous attacks，networks are strongly robust to random attacks，but weakly robust to deliberate attacks，where organizations with high degree values are key to making networks robust.