A　green　and　low-cost　method　to　prepare　high-quality　GaN　(gallium　nitride)　nanowires　is　important　for　the　applications　of　GaN-based　devices　on　a　large　scale.　In　this　work,　high-quality　GaN　nanowires　are　successfully　prepared　by　a　green　plasma　enhanced　chemical　vapor　deposition　method　without　catalyst,　with　Al2O3　used　as　a　substrate,　metal　Ga　as　a　gallium　source　and　N-2　as　a　nitrogen　source.　The　obtained　GaN　nanomaterials　are　investigated　by　using　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM),　transmission　electron　microscopy　(TEM),　Raman　spectroscopy,　and　photoluminescence　(PL)　spectroscopy.　The　XRD　results　demonstrate　that　hexagonal-wurtzite　GaN　is　obtained　and　no　other　phases　exist.　The　SEM　results　show　that　GaN　nanowires　and　hexagonal　GaN　microsheets　are　obtained　at　different　temperatures.　When　the　growth　temperature　is　at　950　degrees　C　(reaction　time　for　2　h),　the　hexagonal　GaN　microsheets　each　with　a　size　of　15　mu　m　are　obtained.　When　the　growth　temperature　is　at　1000　degrees　C(reaction　time　for　2　h),　the　GaN　nanowires　with　the　lengths　in　a　range　of　10-20　mu　m　are　obtained.　With　the　reaction　temperature　increasing　from　0.5　h　to　2　h,　the　lengths　of　GaN　nanowires　increase.　The　TEM　results　suggest　that　the　GaN　nanowires　are　of　high　crystallinity　and　the　growth　direction　of　GaN　nanowires　is　in　the　[0001]　direction.　The　Raman　results　indicate　that　there　exists　a　compressive　stress　in　the　GaN　nanowires　and　its　value　is　0.84　GPa.　Meanwhile,　the　growth　mechanism　of　GaN　nanowires　is　also　proposed.　The　morphologies　of　GaN　nanomaterials　are　tailed　by　the　growth　temperature,　which　may　be　caused　by　Ga　atomic　surface　diffusion.　Ga　atoms　have　low　diffusion　energy　and　small　diffusion　length　at　950　degrees　C.　They　gather　in　the　non-polar　m-plane.　The　(0001)　plane　with　the　lowest　energy　begins　to　grow.　Then,　hexagonal　GaN　microsheets　are　obtained.　When　reaction　temperature　is　at　1000　degrees　C,　the　diffusion　length　of　Ga　atoms　increases.　Ga　atoms　can　diffuse　into　(0001)　plane.　In　order　to　maintain　the　lowest　surface　energy,　the　GaN　nanowires　grow　along　the　[0001]　direction.　The　PL　results　indicate　that　the　obtained　GaN　nanowires　have　just　an　intrinsic　and　sharp　luminescence　peak　at　360　nm,　which　possesses　promising　applications　in　photoelectric　devices　such　as　ultraviolet　laser　emitter.　Our　research　will　also　provide　a　low-cost　and　green　technical　method　of　fabricating　the　new　photoelectric　devices.