Fire-fighting system is an important system to ensure the viability of ships. According to the characteristics of ships, this paper in brief presents a cascading failure definition and cascading failure mechanism of ship fire-fighting system. Combined with the internal environment and external environment of ship fire-fighting system, a evalution index system of cascading failure is established and the index weights are determined by AHP. It finds more important evaluation index through a total weight order. This research provides a theoretical basis for failure prevention and safety management work of ship fire fighting system.