Abstract: In order to ensure that operators can work safely in the FAO (fully automatic operation) area, considering the characteristics and requirements of metro FAO system, Ningbo Metro Line 5 is taken as example, a reasonable overall design scheme of SPKS (staff protection key switch) is proposed. The proposed scheme adopts optimization measures including dividing individual protection zones for entry/exit section lines and turn-back areas, protecting the main line according to up and down directions respectively, adopting double connection point collection, double coil drive and double confirmation of bypass button of SPKS control circuit. The safety and reliability of SPKS circuit design are studied and analyzed. Research results show that the proposed operation scheme can adapt well to complex operation scenarios such as entry/exit lines, improve the flexibility of turn-back operation, and is in accordance with the ′fault-safety′ principle of signaling system.