ZnO　nanorods　were　successfully　prepared　by　hydrothermal　method　using　zinc　nitrate　hexahydrate　and　hexamethylenetetramine　as　raw　materials.　The　effects　of　growth　and　cooling　time　on　the　morphologies　and　sizes　of　final　products　were　investigated.　The　resultant　products　were　characterized　by　SEM,　XRD,　photoluminescence　spectra,　UV-Vis　and　FT-IR　spectrum.　XRD　and　SEM　results　show　that　the　ZnO　nanorods　with　hexagonal　wurtzite　structure　have　been　synthetized　with　average　diameter　of　300　nm　when　the　reaction　time　is　set　to　6　h　and　the　reaction　temperature　is　rapidly　reduced　to　room　temperature.　PL　measurements　show　that　the　samples　have　good　crystal　quality　and　optical　properties.　UV-Vis　spectrum　analysis　reveals　that　ZnO　nanorods　have　the　strong　absorbing　peak　between　200-400　nm.　The　FT-IR　spectra　indicate　that　the　characteristics　absorption　peaks　of　Zn-O　appeared　on　430　cm-1,　which　showed　obvious　red-shifts　compared　with　that　of　pure　ZnO　nanomaterial.　The　field　emission　characteristics　show　that　its　turn-on　field　strength　and　the　field　enhancement　factor　are　2.2　V/μm　and　2550　respectively.　In　addition,　the　maximum　emission　current　density　of　the　ZnO　nanorods　can　reach　to　0.7　mA/cm2　when　the　electric　field　is　4.75　V/μm,　which　is　regarded　as　good　electron　emission　source　for　cold　cathode.