We　develop　an　in-line　distributed　optical　fiber　acoustic　sensor　array　based　on　Sagnac　interferometer　use　it　to　measure　and　locate　leaks　for　the　fluid-filled　(or　gas-　filled)　pipelines　in　real　time.　The　advantage　of　the　sensor　array　is　that　it　can　monitor　two　or　many　pipelines　at　the　same　time.　The　traditional　loop　Sagnac　interferometer　is　changed　into　in-line　structure　by　a　Faraday　rotator　mirror.　The　representation　of　phase　change　caused　by　leakage　is　formulated　for　optic　signal;　the　measuring　principle　and　the　leaking　source　location　method　for　the　sensor　array　are　analyzed.　An　experiment　is　designed　to　detect　and　locate　leaks.　The　results　verify　that　the　system　can　realize　leak　detection　and　locate　leak　accurately,　and　the　error　is　less　than　0.54%.　(c)　2008　Society　of　Photo-Optical　Instrumentation　Engineers.