The present invention discloses a standby power supply circuit for a 2-wire bus intercom system and an apparatus thereof. The standby power supply circuit is separated into two power supply modules; in which the first power supply module is a power supply to standby circuit and the second power supply module is a power supply to operation circuit; said power supply to operation circuit is switched off by a constant current switch when the device load is at the standby status; and said power supply to standby circuit comprises a constant current circuit whose alternating current impedance is very large. The solutions of the present invention achieve larger alternating current impedance for the 2-wire intercom system, which can offer sufficient power for many device loads both in the conditions of operation and standby statuses.