Yb∶YAG (Yb∶Y3Al5O12) crystal with Yb3+ doping level up to 50 at.-% has been grown by Czochralski method. The absorption, emission spectra and fluorescence lifetime of Yb∶YAG crystal at room temperature have also been studied. Two absorption bands are centered at 939 nm and 969 nm of Yb3+, respectively, which are suitable for InGaAs diode laser pumping, and the main fluorescence band is located around 1032 nm. The fluorescence lifetime of Yb∶YAG laser crystal is 390 μs. The spectral parameters of low and high doping Yb∶YAG crystals are compared. The results indicate that Yb∶YAG with high doping concentration is a promising laser material for high power laser output.