The invention relates to an optical gyroscope, in particular to a fiber laser gyroscope. It consists of an ultra-narrow linewidth fiber mode-locked laser, a wavelength division multiplexer, a fiber Sagnac loop, a circulator, a polarizer and a detector, and a difference frequency signal processing circuit. It is characterized in that it uses a semiconductor pump with a pigtail Active fiber ring laser with Sagnac effect composed of laser, isolator, wavelength division multiplexer and gain fiber; two sets of fiber coupler, circulator, ultra-narrow linewidth photon injection fiber mode-locking device, polarizer and detector The mode selection filter output system composed of the device forms the optical path scheme of the fiber laser gyroscope. The photon injection fiber mode-locking technology introduced in the present invention can make the gyroscope work stably in the ultra-narrow linewidth single longitudinal mode laser state, thereby obtaining the high-resolution detection result of the angular rate; The difference can automatically eliminate the zone-locking effect of the laser gyro. As a high-precision gyroscope, the invention can be applied to inertial measurement units of aviation, spaceflight, navigation and land weapons.