To eliminate the gross error in the distributed optical fiber pipeline leakage detecting andprewarning system and to improve the locating accuracy, based on the analysis on the detecting and locating principle, the optical polarization model is established which is based on the equivalent Jones matrix of the single-mode optical fiber birefringence. Model simulation shows that the cause for the gross error is the discrepancy of two signals, which means that the signals acquired by the photodetectors from the same vibroseis are not correlative. According to the theoretical model, the solution of using external polarization controller to change the polarization direction is put forward. It is proved by the experiment that the solution can solve the problem preferably and improve locating accuracy. Furthermore, a theoretical guidance of the system improvement and the adjustment in optical structure is provided based on the theoretical model.