The invention relates to a metal loop wire longitudinal differential protection method in a parallel-connection ice melting mode, and belongs to an extra-high-voltage direct-current transmission direct-current protection system. The metal loop wire longitudinal differential protection method is provided specific for a direct-current transmission system in the parallel-connection ice melting mode. Currents of electrodes 1 and currents of electrodes 2 of a home station and an opposite station are collected, and home station circuit total currents and opposite station circuit total currents are calculated respectively according to the collected currents; the current difference value of the home station and the opposite station is calculated according to the home station circuit total currents and the opposite station circuit total currents; finally, longitudinal differential protection is performed according to the difference value of the circuit total currents of the two stations. The defect of metal loop wire longitudinal differential protection maloperation caused by the fact that only the difference value of metal loop wire currents of the home station and metal loop wire currents of the opposite station is calculated in existing metal loop wire longitudinal differential protection is overcome. According to the method, breakdowns can be fast and accurately judged, and phase-shift locking of the system due to metal loop wire longitudinal differential protection maloperation in the parallel-connection ice melting mode is avoided.