Upconversion　(UC)　phosphor　Tm3+　doped　YF3　nano-crystals　were　prepared　by　hydrothermal　method　under　different　conditions　and　characterized　by　Field　Transmission　electron　microscopy　(TEM),　Scanning　electron　microscopy　(SEM)　and　X-ray　diffraction　(XRD).　Their　UC　luminescence　properties　were　studied　by　fluorescence　spectrophotometer　with　980　nm　diode　laser　excitation,　and　impact　of　different　grain　sizes　and　morphology　on　the　UC　luminescence　intensity　was　discussed.　The　fluorescence　decay　lifetime　was　calculated　by　Multi-exponential　function　fitting　method.　Results　show　that　UC　emission　intensity　was　enhanced　with　the　reduction　of　grain　size,　and　the　decay　lifetime　is　0.60　us.