The invention discloses a compensator and compensation method for transmission delay in optical fiber time frequency transmission. The compensator comprises a central station and a remote terminal, wherein the central station is connected with the remote terminal through optical fibers, the central station comprises a time frequency scale source, a frequency multiplier I, a frequency multiplier II, a filter I, a frequency mixer I, a frequency mixer II, a filter II, a light emitting module I, a combiner, a light receiving module I and an amplifier I, and the remote terminal comprises a wave separator, an optical modulator I, an optical modulator II, a light receiving module II, an amplifier II, a filter III, a phase shifter, a power divider, a light emitting module II and an electrical interface. The compensation method includes the steps that the central station conducts long-distance injection locking on a photoelectric oscillator of the remote terminal, the remote terminal accumulates errors and transmits the errors back to the central station, the central station conducts compensation through phase delay and a fluctuation regulation and control circuit, and therefore the output of the photoelectric oscillator of the remote terminal is locked to the central station. According to the compensator and the compensation method, the asymmetry of two-way delay is eliminated, therefore, the transmission accuracy can not be limited by the measurement accuracy of the system, and accurate long-distance transmission can be conducted.