Abstract: In order to eliminate the impact of negative disturbance on the all-optical-fiber interferential system, a new method to resist time-varying disturbance was proposed. There are two routes of interferential signals with a constant phase difference, by means of simple signal modulation and mathematic computation, to avoid the problem that the useful signal to noise ratio in the single-channel signal easily affected by the differences of optical path bias phase angle and modulation phase difference, while improving the quality of signals. Experiments show that the system can effectively eliminate the disturbing noise without strict requirements on coupler prismatic ratio, and is more practical.