A　distributed　optical　fiber　sensor　based　on　the　principle　of　Sagnac　interferometer　is　developed.　It　is　used　to　detect　pipeline　leakage　and　locate　leakage　point　in　real-time.　The　measuring　principle　and　the　leaking　point　location　method　for　the　technology　are　described.　The　representation　of　phase　change　caused　by　leakage　is　formulated　for　optic　signal.　An　experiment　is　designed　to　verify　the　distributed　optical　fiber　acoustic　sensor.　The　results　verify　that　the　detection　technology　can　detect　pipeline　leakage　effectively　and　locate　leak　point　accurately　in　the　condition　that　the　water　pressure　is　0.3　MPa.