The invention relates to an eigenfrequency tracking measurement method of a Sagnac optical fiber ring of an optical fiber gyroscope, and belongs to the technical field of fiber-optic gyroscopes. The eigenfrequency tracking measurement method comprises the following steps: after going through a coupler and a Y waveguide phase modulator, dividing light into two beams of linearly polarized light, respectively propagating the two beams of linearly polarized light clockwise and anticlockwise along an optical fiber sensing ring, performing sawtooth wave phase modulation and square wave bias phase modulation at the phase modulator and then returning to a Y waveguide position for interference; after processing, demodulating an error signal from an FPGA (field programmable gate array); and adjusting the frequency of a sawtooth wave modulation signal and the frequency of a square wave bias modulation signal according to the intensity of the error signal, wherein the frequency of the sawtooth wave signal is equal to the even number times of the eigenfrequency, and the error signal is zero, and at the moment, the square wave bias modulation frequency is accurately located on the eigenfrequency, the frequency of the sawtooth wave modulation signal is just the even number times of the eigenfrequency, and the square wave bias modulation frequency is equal to the eigenfrequency. According to the method, the purposes of tracking measurement for the eigenfrequency of the optical fiber gyroscope and adjustment of the square wave bias frequency onto the eigenfrequency are realized.