Hydrazine　(N2H4)　has　been　classified　as　an　environmental　contaminant　and　human　carcinogen　owing　to　its　high　toxicity.　Being　exposed　to　high　levels　of　hydrazine　can　cause　irreversible　damage　to　human　bodies.　Hence,　it　is　significant　to　explore　an　effective　method　to　selectively　recognize　and　detect　it.　In　this　work,　a　new　＂turn-on＂　fluorescence　probe,　coumarin-thiophene　(C-T),　was　designed　based　on　PET　(photo-induced　electron　transfer)　mechanism　by　employing　5-chlorothiophene-2-carbonyl　chloride　as　a　electron　donor　and　coumarin　as　a　electron　acceptor.　The　flourescence　could　be　recovered　due　to　the　interruption　of　PET　by　stripping　the　5-chlorothiophene-2-carbonyl　chloride　when　treated　with　hydrazine.　The　mechanism　was　further　verified　through　H-1　NMR　titration　and　spectral　analysis.　Additionally,　The　probe　exhibited　a　high　selectivity　towards　hydrazine　over　other　common　ions　and　amine-containing　species　with　a　distinct　fluorescence　enhancement　at　450　nm.　The　probe　could　operate　over　a　wide　pH　region　(4-10)　with　a　detection　limit　as　low　as　0.0047　mu　M　(1.5　ppb),　Furthermore,　it　could　selectively　detect　hydrazine　in　different　water　samples　which　indicated　its　potential　for　practical　applications.