The invention provides a power supply dynamic adaption overcurrent protection method and system of a subway AC ring network. The protection function is configured on an incoming and outgoing line cabinet of a subway ring network power supply system and a protection device of a buscouple cabinet; the dynamic adaption overcurrent protection action time of an outgoing line protection device is delayed to T2 from T1 if communication between the outgoing line protection device and an incoming line protection device at an adjacent power supply region; if a fault occurs in the outgoing line protection device, the dynamic adaption overcurrent protection action time of the incoming line protection device on the same bus of the outgoing line protection device is delayed to T2 from T1, the incoming line protection device acts when the dynamic adaption overcurrent protection time is delayed to T2 and the fault is not removed, excessively large fault removal range is prevented, and the subway station running reliability is improved.