A system for high-precision long-distance distributed fiber-optic time transfer, comprising a first clock source, a first fiber-optic time transfer unit, N relay and user units, M bidirectional optical amplifying units, a second fiber-optic time transfer unit and a second clock source; wherein N and M are natural numbers greater than or equal to 1; wherein the first clock source is connected to the first fiber-optic time transfer unit through an electrical connection; the first fiber-optic time transfer unit, the N relay and user units, the M bidirectional optical amplifying units, and the second fiber-optic time transfer unit are connected by fiber to form a single-fiber bidirectional series path, the first fiber-optic time transfer unit and the second fiber-optic time transfer unit are respectively located at one and the other end of the single-fiber bidirectional series path, and the order of the N relay and user units and the M bidirectional optical amplifying units on the series path is arbitrary; the second fiber-optic time transfer unit is connected to the second clock source through an electrical connection; a timing signal output by the first clock source is transmitted by the first fiber-optic time transfer unit, along the single-fiber bidirectional series path, passes through an optical-electric-optical relay of the N relay and user units, and an optical amplification of the M bidirectional optical amplifying units, and reaches the second fiber-optic time transfer unit; a timing signal of the second clock source is transmitted by the second fiber-optic time transfer unit, along the single-fiber bidirectional series path, passes through the optical-electric-optical relay of the N relay and user units in reverse, and the optical amplification of the M bidirectional optical amplifying units, and reaches the first fiber-optic time transfer unit; the first fiber-optic time transfer unit is configured to measure the time interval between the timing signal from the second fiber-optic time transfer unit and the timing signal of the first clock source, and to transmit the time interval to the N relay and user units and the second fiber-optic time transfer unit through the single-fiber bidirectional series path; the second fiber-optic time transfer unit is configured to measure the time interval between the timing signal from the first fiber-optic time transfer unit and the timing signal of the second clock source, and to transmit the time interval to the N relay and user units and the first fiber-optic time transfer unit through the single-fiber bidirectional series path; the first fiber-optic time transfer unit, the N relay and user units, and the second fiber-optic time transfer unit are configured to obtain the time difference between the local timing signal of each unit and the timing signal of the first clock source according to the measured time interval information they received, thereby realizing high-precision distributed time transfer. a timing signal output by the first clock source is transmitted by the first fiber-optic time transfer unit, along the single-fiber bidirectional series path, passes through an optical-electric-optical relay of the N relay and user units, and an optical amplification of the M bidirectional optical amplifying units, and reaches the second fiber-optic time transfer unit; a timing signal of the second clock source is transmitted by the second fiber-optic time transfer unit, along the single-fiber bidirectional series path, passes through the optical-electric-optical relay of the N relay and user units in reverse, and the optical amplification of the M bidirectional optical amplifying units, and reaches the first fiber-optic time transfer unit; the first fiber-optic time transfer unit is configured to measure the time interval between the timing signal from the second fiber-optic time transfer unit and the timing signal of the first clock source, and to transmit the time interval to the N relay and user units and the second fiber-optic time transfer unit through the single-fiber bidirectional series path; the second fiber-optic time transfer unit is configured to measure the time interval between the timing signal from the first fiber-optic time transfer unit and the timing signal of the second clock source, and to transmit the time interval to the N relay and user units and the first fiber-optic time transfer unit through the single-fiber bidirectional series path; the first fiber-optic time transfer unit, the N relay and user units, and the second fiber-optic time transfer unit are configured to obtain the time difference between the local timing signal of each unit and the timing signal of the first clock source according to the measured time interval information they received, thereby realizing high-precision distributed time transfer.