Abstract: This paper analyzes the cause of the 24th harmonic current in the DC feeder of subway as well as the change of the 24th characteristic harmonic current amplitude after a fault occurs.A protection method for DC feeder in subway is proposed based on the 24th harmonic current amplitude.The protection method is based on the principle that the amplitude of characteristic harmonic increases after a fault,which reflects the occurrence of a fault on the DC feeder of subway.This method sets different protection criteria according to whether the locomotive is running before the fault,to avoid the false operation of protection in the case of lifting the pantograph and passing the insulation.This paper provides the action criterion,implementation process,and setting value selection principle of the protection method,and the MATLAB/Simulink simulation verifies that the protection method can correctly identify faults on the DC feeder.