Optics　quality　(Er3+:Yb3+)-doped　yttrium　aluminum　garnet　(Y3Al5O12,　YAG)　crystals　were　grown　by　the　Czochralski　method.　The　absorption　spectrum　and　upconversion　fluorescence　spectrum　of　the　crystals　were　measured.　According　to　the　theory　of　Judd-Ofelt,　the　phenomenological　intensity　parameters　of　Er3+　in　Er3+　:　Yb3+　:　YAG　crystals,　e.g.:　Ω2=1.0741　×　10-20　cm2,　Ω4=1.2953　×　10-20　cm2,　Ω6=0.9238　×　10-20　cm2,　were　calculated　with　the　absorption　spectrum　measurement　results.　Based　on　these　Ωλ　values,　the　fluorescence　branching　ratio,　radioactive　lifetime,　and　integrated　emission　cross　section　of　some　transitions　were　estimated.　The　transition　of　4F9/2&rarr4I15/2　at　679　nm　was　introduced　as　a　new　laser　channel　to　be　studied.