The invention discloses a bidirectional optical amplifier applied to an extra-long-distance high-precision time transmission system. The bidirectional optical amplifier comprises a first polarizer, asecond polarizer, a first unidirectional Faraday rotator, a second unidirectional Faraday rotator, a birefringence beam splitter and a unidirectional optical amplifier. The first polarizer, the firstunidirectional Faraday rotator, the port 1 and the port 2 of the birefringence beam splitter, the unidirectional optical amplifier, the port 3 and the port 4 of the birefringence beam splitter, the second unidirectional Faraday rotator and the second polarizer form a first amplification optical path. The second polarizer, the second unidirectional Faraday rotator, the port 4 and the port 2 of thebirefringence beam splitter, the unidirectional optical amplifier, the port 3 and the port 1 of the birefringence beam splitter, the first unidirectional Faraday rotator and the first polarizer form asecond amplification optical path.