Abstract: For resonator fiber optic gyro (R-FOG), resonance frequency locking is a key technique at detecting the gyro signal. The stability of resonance frequency locking determines the output performance of the gyro, especially in the long-term test. According to the transmission theory of fiber ring resonator (FRR), the resonance characteristics and the first harmonic were analyzed; the R-FOG system was set up. The first harmonic demodulation signal derive from the experiments using the sine wave phase modulation technique; the drift errors of traditional analog proportional-integral PI consisting of operational amplifiers were analyzed. On this basis, T-type feedback network was applied in resonance frequency locking of R-FOG. The drift error was suppressed effectively and better result was obtained. The stability of resonance frequency locking for 4 000 s is superior to 910-12 by Allan variance analysis.