A　large　amount　of　tin　oxide　(SnO2)　nanowire　arrays　were　synthesized　on　the　flexible　conductive　carbon　fiber　substrate　by　thermal　evaporation　of　tin　powders　in　a　tube　furnace.　The　temperature,　as　well　as　the　flow　rate　of　the　carrier　N2　gas　and　the　reaction　O2　gas,　plays　an　important　role　in　defining　the　morphology　of　the　SnO2　nanowires.　Morphology　and　structure　of　the　as-grown　SnO2　samples　are　characterized　by　scanning　electron　microscopy　(SEM),　transmission　electron　microscopy　(TEM),　energy　dispersive　spectroscopy　(EDS),　and　X-ray　diffraction　(XRD).　Results　show　that　all　the　samples　possess　a　typical　rutile　structure,　and　no　other　impurity　phases　are　observed.　The　morphology　changes　from　rod　to　wire　with　the　increase　of　reaction　temperature.　Ratio　of　length　to　diameter　of　the　nanowires　increases　first　and　then　decreases　with　the　flow　ratio　of　N2/O2　gas.　The　optimum　synthesis　conditions　of　SnO2　nanowire　are:　reaction　temperature　780,　N2　and　O2　flow　rates　being　300　sccm　and　3　sccm　respectively.　In　our　growth　process,　the　nanowire　grows　mainly　due　to　the　vapor-liquid-solid　(VLS)　growth　process,　but　both　the　VLS　process　and　surface　diffusion　combined　with　a　preferential　growth　mechanism　play　the　important　role　in　morphology　evolution　of　the　SnO2.　Field　emission　measurements　for　Samples　1-6　are　carried　out　in　a　vacuum　chamber　and　a　diode　plate　configuration　is　used.　Relationship　between　the　growth　orientation,　aspect　ratio,　density　and　uniformity　of　the　arrays　and　field　emission　performances　will　be　investigated　first.　Results　reveal　that　the　field　emission　performance　of　SnO2　nanostructures　depends　on　their　morphologies　and　array　density.　The　turn-on　electric　field　(at　the　current　density　of　10　μA/cm2)　decreases　and　the　emission　site　density　increases　with　tin　oxide　array　density,　and　the　turn-on　electric　field　of　Sample　5　(synthesized　at　780,　nitrogen　and　oxygen　flow　rates　being　300　sccm　and　3　sccm　respectively)　is　about　1.03　V/μm　at　a　working　distance　of　500　μm.　By　comparison,　for　the　turn-on　electric　fields　of　the　not　well-aligned　SnO2　nanowire　arrays　we　have　1.58,　2.13,　2.42,　1.82,　and　1.97　V/μm　at　500　μm.　These　behaviors　indicate　that　such　an　ultralow　turn-on　field　emission　and　marked　enhancement　in　β(~4670)　can　be　attributed　to　the　better　orientation,　the　good　electric　contact　with　the　conducting　fiber　substrate　where　they　grow,　and　the　weaker　field-screening　effect.　Our　results　demonstrate　that　well-aligned　nanowire　arrays,　with　excellent　field-emission　performance,　grown　on　fiber　substrate　can　provide　the　possibility　of　application　in　flexible　vacuum　electron　sources.　©　2015,　Chinese　Physical　Society.