The invention provides a bidirectional 
quantum time synchronization method based on frequency entangled light sources. Two entangled light sources with same 
wavelength are placed at a place A and a place B respectively, and 
signal lights generated by the entangled light sources pass through an 
optical fiber circulator, are transmitted in opposite directions through a same 
optical fiber, and are detected by detectors at the opposite places; idle lights generated by the entangled light sources are detected by a 
detector at a uniform place of the entangled light sources; a 
clock a at the place arecords the time (tij} and time (t2j} for photons emitted by the entangled 
light source at the place a to reach the detectors at two places, and a 
clock b at the place b records time (t3j} and time (t4j} for photons emitted by the entangled 
light source at the place b to reach the detectors at two places, wherein j is representative of jth 
photon; the (tij} and (t2j} are subjected to cross-correlation operation to obtain t2-t1; the (t3j} and (t4j} are subjected to cross-correlation operation to obtain t4-t3; the 
clock difference t0 between the clock a and the clock b is equal to half of the difference of (t2-t1) and (t4-t3). The bidirectional 
quantum time synchronization method based on the frequency entangled light sources is high in 
measurement precision, and an applied device is simplein structure.