Extrinsic fiber Fabry-Perot (F-P) sensor could detect partial discharge in liquid-solid composite insulation, but natural frequency and sensitivity of F-P sensor are affected by viscous damping and added mass of liquid insulation. We use finite element analysis method to simulate the amplitude-frequency response characteristics of F-P sensor under forced vibration in air and liquid insulation medium, and analyze the amplitude-frequency characteristics and sensitivity of F-P sensor at different temperatures. We propose the F-P sensor with isolating liquid insulation structure to eliminate the effect of medium and design an experiment system to measure amplitude-frequency response curves of F-P sensors at different temperatures. The experimental results show that due to viscous damping and added mass of liquid, natural frequency of F-P sensor in liquid insulation transformer oil is 0.58 times of that in air, the bandwidth of amplitude-frequency curve becomes wider, and the harmonic response amplitude decreases. Furthermore, the temperature of liquid medium increases, the natural frequency of F-P sensor increases, the bandwidth of amplitude-frequency becomes narrower, and the harmonic response amplitude and sensitivity increase. It’s found that F-P sensor with isolating liquid insulation structure are immune to media viscous damping and additional mass.