NiSe2　nanowire　(NW)　arrays　grown　on　flexible　carbon　fiber　paper　(CFP)　were　synthesized,　for　the　first　time,　through　a　novel　thermal　selenization　method　in　vacuum　instead　of　flowing　inert　gas.　The　ultrathin　NiSe2　NWs　uniformly　cover　the　CFP,　contributing　to　the　large　surface　area　and　fast　charge　transportation.　Desirably,　this　binder-free　and　hierarchical　electrode　shows　favorable　activity　for　hydrogen　evolution　reaction　(HER).　It　only　requires　an　overpotential　of　172　mV　to　afford　the　current　density　of　100　mA　cm(-2)　in　0.5　M　H2SO4,　corresponding　to　a　low　Tafel　slope　of　32.44　mV　dec(-1).　After　1000　continuous　cycles,　the　HER　activity　of　NiSe2　NWs　is　well-maintained.　Moreover,　the　current　density　remains　unchanged　in　prolonged　electrolysis,　indicating　an　excellent　durability　of　NiSe2　NWs.　The　novel　preparation　method　described　in　this　study　could　inspire　future　work　on　the　synthesis　of　transition-metal　dichalcogenides　with　high　purity　and　ultrasmall　nanostructure　toward　improved　electrocatalytic　activity.