In　this　paper,　the　sensitivity　and　uncertainty　analysis　model　has　been　proposed　and　implemented　in　the　NECP-ONION　system,　which　is　capable　of　performing　the　3D　online　power-distribution　monitoring　for　PWR　by　applying　the　harmonics　expansion　method.　A　new　method　called　the　analytical　method　is　used　to　quantify　the　relative　sensitivity　coefficients　of　the　monitored　power　distributions　with　respect　to　the　detector　signals;　then　the　＂sandwich＂　rule　is　used　to　quantify　the　uncertainties　of　the　monitored　power　distributions　with　the　sensitivity-analysis　results　based　on　the　uncertainty-propagation　method.　The　BEAVRS　benchmark　is　used　to　verify　the　sensitivity　and　uncertainty　analysis　capability　in　NECP-ONION.　The　results　of　the　direct　numerical　perturbation　method　are　used　as　reference　to　verify　the　sensitivity　coefficients　calculated　with　the　analytical　method.　The　results　of　the　statistical　sampling　method　and　the　analytical　method　are　compared　to　each　other　for　the　uncertainty　verification.　Then,　the　sensitivity　and　uncertainty　analyses　with　various　expansion　orders　of　harmonics　and　core　burnup　levels　are　carried　out.　Numerical　results　show　that,　the　expansion　order　is　the　trade-off　of　the　monitoring　accuracy　and　uncertainty,　while　the　sensitivity　and　uncertainty　analysis　is　useful　for　the　determination　of　the　expansion　order.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.