Optical interferometer extinction ratio determines the sensitivity of interferometric fiber optic sensor system to a large extent and further determines the range of applications and prospects of interferometer. The outline of the current ultra-long distance optical fiber interferometric sensing system development status, the theoretical analysis of the impact of polarization on the optical fiber sensing system, and a variety of factors which can affect the polarization are given. The squeeze-type polarization controller based on photoelastic effect is used to tune the extinction ratio of the system by providing radial stress to fiber interferometer arm, to tune system polarization state dynamically, which makes it possible to molerate the extinction ratio of a long-distance optical fiber sensing system at one point. A novel tuning method to tune the sensitivity of long-distance fiber optic sensing system is proposed, and the range of dynamic extinction ratio of tuning is 0.21～11.03 dB.