The　morphology,　microstructure　and　field　emission　(FE)　properties　of　tetrapod　shaped　Sn　doped　ZnO　(T-SZO)　nanostructures　grown　for　different　times　were　investigated.　It　is　found　that　the　morphology,　particularly　the　aspect　ratio　of　the　T-SZO,　can　be　controlled　by　adjusting　the　growth　time　and　that　the　aspect　ratio　affects　its　FE　properties.　The　aspect　ratio　increases　first　with　the　growth　time,　and　after　90　s,　a　new　series　of　T-SZO　with　smaller　size　and　lower　aspect　ratio　appear,　leading　to　the　deterioration　of　the　FE　properties.　The　sample　grown　for　90　s　exhibits　the　highest　aspect　ratio　of　16:5　and　the　lowest　turn　on　field　of　1.82　V　mu　m(-1).