The invention relates to a relay protection method of a power supply line. Equipment used in the method includes an acquisition unit, an alternating-current sampling unit, a signal conversion unit, a storage unit, a display unit, a processing unit, a relay protection device, a control unit, a wireless communication unit, a sending module and a terminal processing unit. According to the method, the situation that whether a relay protection result is needed is judged according to real-time frequency analysis results of voltage parameters and alternate-current signals, so that the relay protection accuracy is increased. Through wireless transmission, the section position in which faults occur is accurately determined according to collected fault signals, and protection ranges and protection modes of relay protection devices which are away from a fault section at different section distances are determined, so that the mistaken operation of bypassing the upper stage and the protection ranges of the relay protection devices is avoided, thereby simplifying relay protection control and protection setting methods of the power supply line.