Abstract: People and objects are occasionally caught between the subway platform door and the train door, which puts forward higher requirements for the safety of the gap detection device. In order to effectively reduce the potential safety problems caused by the gap between the platform door and the train door in the fully automatic operation line, this paper analyzed the linkage mode between the gap detection device and the relevant system of the train operation for the fully automatic operation line, and proposed the optimization scheme of the linkage mode between the gap detection device and the relevant system based on the practice of the second phase project of Tianjin Metro Line 6. The paper used this scheme to optimize the original interface circuit, added the "door status" hard line signal, improved the control flow, optimized the gap detection start time. It provides a new solution for the safe of the fully automatic operation line.