In　the　present　paper　the　authors　firstly　measured　the　absorption　spectra　of　Er3+　in　the　sample　Er3+　:　YVO4　(0.　5%)　then　calculated　the　intensity　parameters　are　calculated　by　using　the　Judd-Ofelt　theory.　After　that　the　authors　dealed　with　some　predicted　spectroscopic　parameters,　such　as　the　oscillator　strength,　spontaneous　radiative　transition　rate,　branching　ratio　and　integrated　emission　cross　section.　And　Er　:YVO4　crystal　application　value　has　been　analyzed　with　the　optical　parameters.　Especially　there　are　large　oscillator　strengths　and　large　integrated　emission　cross　sections　in　the　transitions　of　I-4(13/2)-＞　I-4(15/2),　H-2(11/2)-＞　I-4(15/2),　S-4(3/2)-＞　I-4(15/2),　F-4(9/2)-＞　4I(15/2).　So,　they　are　more　worth　of　attention.,Moreover,　by　comparing　the　Er-doped　yttrium　vanadate　crystal　and　other　Er-doped　crystal　optical　properties,　the　authors　can　see　the　advantages　of　YVO4　as　laser　crystal.　Finally,　the　authors　discussed　the　splitting　of　the　energy　levels　of　Er3+　in　the　crystal　YVO4　based　on　the　group　theory.