The invention discloses a method and device for stabilizing a fiber optic gyroscope and maintaining a scale factor. A microminiature thermistor is integrated in a Y-waveguide modulator to monitor the Y-waveguide temperature, a scale factor compensate algorithm is inserted into a fiber optic gyroscope all-digital signal processing algorithm to form a fiber optic gyroscope scale factor stabilizing device, and the fiber optic gyroscope scale factor can be stabilized under the action of wide temperature range and radiation. According to the method and device for stabilizing the fiber optic gyroscope and maintaining the scale factor, a mathematical model which is irrelevant to the wave length of the fiber optic gyroscope scale factor is established, a temperature characteristic equation of an intrinsic modulation parameter m which is irrelevant to the wave length of a Y-waveguide is obtained through an experiment, by means of the fine compensation technology, the fiber optic gyroscope scale factor is stabilized, the influence of light source wavelength on Y-waveguide half-wave voltage control or compensation precision is eliminated, and requirements of a high-precision fiber optic gyroscope for light source wavelength stability is broadened. According to the method for stabilizing the fiber optic gyroscope and maintaining the scale factor, under the situation that the gyroscope cost and complexity are not increased obviously, the stability of the scale factor of the fiber optic gyroscope is maintained, and the problems that the fiber optic gyroscope scale factor used in space is not stable and cannot be controlled are solved.