As　the　main　transportation　facilities,　such　as　petroleum,　natural　gas,　city　water,　and　among　others,　the　pipeline　has　been　concerned　extensively　for　its　safety　in　operation.　Meanwhile,　to　find　and　locate　the　positions　of　the　persistent　small-scale　leakage　of　the　pipeline　is　one　of　the　major　issues　and　difficulties　faced　by　the　safe　operation　of　the　pipeline.　When　Sagnac　fiber　interferometer　is　in　the　use　of　monitoring　and　positioning　of　a　small　leak　on　pipeline,　the　interference　result　of　the　two　coherent　laser　beams　in　Sagnac　ring　will　be　affected　by　the　random　change　of　light　polarization,　thereby　affecting　the　interferometer　performance　of　linear　Sagnac　fiber　optic　interferometer.　A　new　method　is　proposed　to　suppress　the　influence　of　random　change　of　polarization　on　Sagnac　interferometer.　By　modifying　the　structure　of　interferometer,　an　optical　depolarizer　is　introduced　into　the　Sagnac　ring　to　improve　the　operational　stability.　Experimental　results　show　that　this　method　is　a　good　solution　to　solve　the　deterioration　of　sensitivity　caused　by　polarization　fading.