The invention discloses a fiber passage-based input method of a thermal spare line combined emergency power supply. The fiber passage-based input method applied to the following circuits that 1, a first circuit of 10kV and a second circuit of 10kV are respectively connected to a substation A station of 220kV and a substation B station of 220kV, a circuit breaker 4DL is arranged a power side of thefirst circuit, a circuit breaker 1DL is arranged at a load side of the first circuit, one end of the second circuit is connected with a 110kV bus of the substation B station, the other end of the second circuit is connected with an II-segment bus of a substation C station, a circuit breaker 5DL is arranged at a power side of the second circuit, a circuit breaker 2DL is arranged at a load of the second circuit 2, a segment or an inner bridge circuit breaker 3DL is arranged between an I-segment bus and the II-segment bus of the substation C station, and emergency power supply automatic input devices are arranged at 110kV sides of the substation A station, the substation B station and the substation C station. By the fiber passage-fiber input method, the problems of excessively high capacitance reactive power of a substation and reverse power transmission of a power grid are solved, the voltage level of the substation is improved, excessively local high voltage of the power grid is prevented, and the integral running level of the power grid is improved.