GdVO4　single　crystal　co-doped　with　Yb3+　and　Er3+　was　grown　by　the　Czochralski　method.　The　X-ray　powder　diffraction　pattern　of　Yb,Er:GdVO4　crystal　confirms　that　the　as-grown　crystal　is　isostructural　with　pure　GdVO4　crystal.　Its　polarized　absorption　spectra　and　non-polarized　fluorescence　spectra　were　measured　at　room　temperature.　The　absorption　band　at　984　nm　for　pi-polarization　has　an　FWHM　of　about　36　nm,　which　is　favorable　for　InGaAs　LD　laser　pumping.　The　spectrum　properties　of　Er3+　in　Yb,　Er:　GdVO4　crystal　were　investigated　based　on　Judd-Ofelt　theory.　There　is　strong　energy　transfer　from　Yb3+　to　Er3+　in　this　crystal.　When　excited　with　980　nm　radiation,　this　crystal　emitted　strong　fluorescence　at　about　1529　nm　and　552.5　nm.　The　total　energy　transfer　rate　and　efficiency　from　Yb3+　to　Er3+　is　3.33　ms(-1)　and　67%,　respectively.　The　energy　transfer　between　Er3+　and　Yb3(+)　ions　is　a　multistep　transfer　process,　and　was　investigated　based　on　a　random-walk　model.　The　investigation　result　shows　that　there　is　strong　cooperative-sensitization　effect　from　Yb3+　to　Er3+,　which　is　the　main　upconversion　energy-transfer　process　in　this　crystal.