Dy2Ti2O7　(DTO)　crystal　with　magneto-optical　effect　has　been　grown　by　Czochralski　method.　Two　DTO　wafers　with　different　oxygen　vacancy　concentrations　were　prepared　by　annealing　in　oxygen　or　ammonia　atmospheres.　The　effect　of　oxygen　vacancy　concentration　on　the　absorption　spectra　of　DTO　crystal　was　investigated　by　first-principles　calculation　based　on　the　density　functional　theory.　It　is　found　that　the　absorption　loss　of　DTO　annealed　in　oxygen　atmosphere　is　about　twice　as　high　as　that　of　DTO　annealed　in　ammonia　atmosphere　in　the　wavelength　of　380-580　nm　at　room　temperature.　Based　on　their　identical　Faraday　rotation　angle,　the　magneto-optical　figures　of　merit　of　DTO　annealed　in　ammonia　atmosphere　are　about　twice　as　large　as　that　of　DTO　in　oxygen　atmosphere　in　the　380-580　nm　range.　The　corresponding　results　reveal　that　oxygen　vacancy　concentration　plays　a　significant　role　in　the　absorption　spectra　of　DTO　crystal,　and　DTO　with　high　oxygen　vacancy　concentration　may　be　a　promising　material　for　magneto-optical　devices　especially　in　the　400-700　nm　range.　(C)　2014　Published　by　Elsevier　B.V.