The invention relates to a small current grounding fault line selection method and device in a double-bus operation mode. The method includes the steps that feeder line disconnecting switch node signals, zero-sequence current signals and bus PT voltage signals are collected in real time; according to information of the feeder line disconnecting switch node signals, characteristics of bus segments which feeder lines belong to are classified; according to a classification result of the feeder lines, the PT signals of the bus segment I and the bus segment II and the zero-sequence current signals of the feeder lines belonging to the bus segments are extracted, and small current grounding fault line selection is monitored in real time. The device comprises a feeder line disconnecting switch node signal obtaining module, a zero-sequence current signal collecting module, a bus PT voltage signal collecting module and a main CPU module. By means of the access of the feeder line disconnecting switch node information, the characteristics of the bus segments which the feeder lines belong to are classified in real time, so that the effect of self-adaption to different operation modes is achieved, and the reliability of fault line selection is ensured.