The phase modulation technique is the key technique to obtain the angular rate in resonator fiber optic gyro (R-FOG). Adopting the appropriate modulation parameters, the performance of the gyro can be greatly improved. Based on the phase modulation spectroscopy expression, and the relationship between the amplitude of modulated carrier signal and the amplitude of phase modulation voltage, the method for determining the optimized phase modulation parameters was proposed. Using the method, the backreflection noise can be effectively suppressed, while the optimized sensitivity of the gyro can also be ensured; The half-wave voltage of the modulator was measured using the self-heterodyne interferometer technique with sine wave phase modulation. And the relationship between the amplitude of modulated carrier signal and the amplitude of phase modulation voltage was obtained, which was consistent with the theoretical analysis; The fiber ring resonator(FRR) was composed of a 12 m length polarization maintaining fiber and a polarization maintaining fiber coupler with the coupling ratio 50％. The diameter of the resonator was 0.15 m. The rotation experiments under various angular rates were conducted, and the dynamic range and output nonlinearity of the R-FOG were ±480 (°)/s and 3%, respectively.