The invention relates to a 1553B branch line relay and a relay processing method for a 1553B signal. The 1553B branch line relay comprises a connector A8, an isolation transformer A9, a 1553B bus transceiver A10, a programmable logic device 7, a 1553B bus transceiver B11, an isolation transformer B12, a coupling transformer 13 and a connector B14, wherein the isolation transformers A9 and B12 are used for performing level conversion and isolation on a signal; the 1553B bus transceivers A10 and B11 are used for performing bidirectional conversion on a Manchester type II two-phase differential signal and a complementary CMOS level signal; the coupling transformer 13 is used for coupling and transforming; the programmable logic device 7 is used for performing bidirectional receiving, filtering, shaping and forwarding on the 1553B signal to complete a signal relay function. The 1553B branch line relay provided by the invention can achieve the purpose of prolonging transmission distance of a stub line easily in the situation of ensuring the signal transmission quality.