Aiming　at　real-time　monitoring　of　the　long　distance　pipeline　and　security　warning　of　perimeter,　distributed　fiber　sensing　security　early　warning　system　based　on　dual-Sagnac　interferometer　is　built,　including:　dual-Sagnac　interferometer　optical　path　system　and　control　and　detect　software　based　on　LabVIEW　platform.　The　optical　phase　modulation　principle　of　external　disturbance　signals　generated　by　pipeline　damage　and　perimeter　intrusion　and　locating　principle　by　amplitude　of　frequency　domain　method　are　analyzed.　The　zero-crossing　number　distribution　of　impulse　disturbance　signal　and　continuous　disturbance　signal　is　studied.　The　software　of　warning　algorithm,　locating　algorithm　and　signal　discriminating　algorithm　based　on　the　principle　is　developed　and　studied　experimentally.　The　results　of　experiment　show　that　the　system　can　realize　real-time　monitoring,　locating　and　signal　discriminator　of　the　external　disturbance.　The　system　has　the　advantages　of　high　positioning　accuracy,　stability　and　reliability　and　easy　operation,　and　a　wide　application　prospects　in　engineering.