The invention discloses a light frequency transmission used all-fiber narrow linewidth fiber laser device and the method thereof. The device of the invention comprises a laser, a first frequency shift device, an isolator, a first Y type coupling device, an X type coupling device, an attenuator, a first Faraday rotating mirror, a second Y type coupling device, a second Faraday rotating mirror, a second frequency shift device, a time-delay fiber, an optical fiber amplifier, a third frequency shift device, a third Faraday rotating mirror, a photoelectric detector, a band pass filter, an oscilloscope, and a frequency synthesizer. According to the invention, under the condition that the frequency discrimination precision of an interferometer is reduced, the length of the time-delay optical fiber could be shortened; the frequency discrimination precision could be increased; the cost can be reduced and the device can be transported.