Abstract: The 6502 electric centralized circuit is the important foundation of railway signal interlocking system and interlocking logic. In view of the flash signal of the hump auxiliary repeater signal in the 6502 electric centralized circuit after the hump auxiliary signal opens the forward signal, this article analyzed the principle of hump auxiliary repeater signal display circuit, and studied the cause of the flash signal of the hump auxiliary repeater signal. From the point of view of whether the break of the advance signal filament of the auxiliary signal of the hump drives the LXJ, the article put forward four modification schemes, and compared the modification range of the original 6502 electric centralized circuit by four schemes, carried out the test in the North Fuyang Three Field. The results show that scheme 4 meets the fault - safety processing principle, which can provide reference for the modification of the subsequent interlocking software related problems.