Bandgap　engineering　has　been　a　powerful　technique　for　manipulating　the　electronic　and　optical　properties　of　semiconductors.　In　this　work,　a　systematic　investigation　of　the　electronic　properties　of　[0001]　GaN　nanowires　was　carried　out　using　the　density　functional　based　tight-binding　method　(DFTB).　We　studied　the　effects　of　geometric　structure　and　uniaxial　strain　on　the　electronic　properties　of　GaN　nanowires　with　diameters　ranging　from　0.8　to　10　nm.　Our　results　show　that　the　band　gap　of　GaN　nanowires　depends　linearly　on　both　the　surface　to　volume　ratio　(S/V)　and　tensile　strain.　The　band　gap　of　GaN　nanowires　increases　linearly　with　S/V,　while　it　decreases　linearly　with　increasing　tensile　strain.　These　linear　relationships　provide　an　effect　way　in　designing　GaN　nanowires　for　their　applications　in　novel　nano-devices.　(C)　2016　Author(s).