Abstract: The resonator fiber optic gyro will be the next-generation fiber-optic gyro following the interferometric fiber optic gyroscope due to its small size, high sensitivity, low power consumption, high reliability, and long life. As the core sensitive unit of resonator gyro, characteristics of transmission spectrum and the corresponding frequency discriminator curve in optical resonator become the key to improving the detection sensitivity of the optical gyro system. The experimental system is designed and built. The splitting ratio of the fiber coupler is 50:50. The fiber ring resonator is made by polarization maintaining fiber whose diameter and length are 17 cm and 2.2 m respectively. Piezoelectric transducer of narrow linewidth laser (linewidth is less than 1 kHz) is scanned by direct-current high voltage amplifier whose scanning frequency and voltage are 20 Hz and 1 V respectively. The analog circuit feedback system is adopted with proportional integral locking technique, so the output frequency of the laser can track the frequency of the resonator in real time. The transmission spectrum and discriminator curve of the fiber ring resonator are analyzed in two different cases. Firstly, the modulation voltages are 2 V and 4 V with a modulation frequency from 100 kHz to 4 MHz; Secondly, the modulation frequency is 900 kHz with a modulation voltage from 2 V to 10 V. Different varieties of seven parameters are obtained, such as the depth of resonance, the full width at half-maximum, the bandwidth, the dynamic range of linear zone, the quality factor, the scale factor and the precision of lock-in frequency. Moreover, three optimum modulation frequency and matched modulation voltage are obtained under static test conditions. These conclusions provide a guidance for further study on laser modulation effect on the spectrum of fiber ring resonators.