The invention belongs to the technical field of line selection function testing for power systems, specifically to a method for detecting a small disturbance analysis line selection apparatus based on RTDS. A simulation model is built according to on-site real parameters of a transformer substation, and different faults are built in the simulation model to allow the simulation model to output corresponding current signals and voltage signals according to different grounding faults. A RTDS signaling channel outputs fault voltage and current in accordance with on-site reality to a power amplifier for amplification, the small disturbance analysis line selection apparatus upon reception of amplification signals feeds back to the simulation model for adjusting compensating ratio through the RTDS signaling channel, and the small disturbance analysis line selection apparatus realizes fault line selection according to signal variance. The method detects small disturbance analysis line selection apparatus in a power distribution network, and accurately determines the line selection capability of the line selection apparatus.