The UV, visible and IR absorption spectra of annealed and as grown Yb:YAG grown by Czochralski technique were measured, and some changes of absorption bands and shifts of absorption peaks are observed and discussed. With the disappearance of broad absorption bands of color center at 370 nm and 625 nm, the new absorption band at 254 nm of annealed Yb:YAG is probably the result of change of color center. The little shifts of absorption peaks at 220 nm and 940 nm are regarded as the result of crystal lattice deformation, which was proved by X ray diffraction. In laser experiment of Yb:YAG crystals, the influence of doping level on laser performance has been observed.