The invention discloses a broadband linear frequency modulation narrow linewidth fiber laser and an implementation method thereof. The implementation method comprises the steps that: a narrow linewidth seed source outputs linear polarization continuous laser with a wavelength of 1.5 microns, a radio frequency signal source generates a linear frequency modulation signal and sends the linear frequency modulation signal to a modulator drive, and the modulator drive loads the linear frequency modulation signal and a bias voltage to a double-parallel phase modulator; an output end of the narrow linewidth seed source is connected with the double-parallel phase modulator, the laser experiences linear frequency modulation in the double-parallel phase modulator, the output end of the double-parallel phase modulator is connected with an optical beam splitter, the output end of the optical beam splitter outputs a part of modulated laser to serve as radar local oscillation light, the output of the optical beam splitter is connected with an optical fiber amplifier, and the amplified laser is output from the output end of the optical fiber amplifier. The broadband linear frequency modulation narrow linewidth fiber laser is narrow in linewidth, large in modulation bandwidth, capable of meeting the use requirements of a synthetic aperture laser radar and a linear frequency modulation continuous wave laser radar, high in modulation speed and high in modulation linearity.