Abstract: Taking Nanning Rail Transit Line 5 (′Line 5′ in short) as the engineering background, the key factors affecting the tunnel interval safety of Line 5 under FAO (fully automatic operation) mode are discussed, the monitoring and prevention of flood and tunnel interval external intrusion are analyzed, and solutions currently available in the industry are summarized. By using video intelligent analysis, array fiber grating sensing, big data analysis as well as other technologies, the intelligent flood early warning system of urban rail transit line network and the intelligent monitoring system of tunnel interval external intrusion based on grating array could be built, which enables the online monitoring and early warning of rail transit FAO line safety status including tunnel interval flood and external intrusion.