The invention discloses a method for generating a frequency modulation signal based on light injection locking. A first laser, a second laser, a first microwave source, a second microwave source, a microwave amplifier, a first coupler, a second coupler, a first polarization controller, a second polarization controller, an isolator, an intensity modulator, a circulator, an acousto-optic frequency shifter and a photoelectric detector are included. The temperature and current parameters of a first laser are adjusted to modulate the first laser, wherein one path modulates an optical signal into asideband through an intensity modulator, and then injects and locks the modulated sideband of the optical signal into a second laser without an isolator, so that the phase of the second laser is locked to a high-order sideband of the first laser; the other path outputs a signal of which the frequency can be linearly changed through an acousto-optic frequency shifter; and then, the two paths of light are coupled by the second coupler, the output end of the second coupler and the photoelectric detector beat frequency to generate a frequency modulation signal with tunable high-frequency broadband, and the frequency modulation signal has the advantages of continuous phase and high stability.