The formation and development of detects in Nd:YAG crystals grown by TGT have been studied systematically with different methods. According to the defect formation mechanism, the high quality area within crystal boules can be enlarged notably after reasonable modification of the growth parameters. Single transverse mode and single longitudinal mode laser output have been obtained easily from high dopant （Nd2O3 1wt％） and high optical homogeneneous laser rods. However, the effect of interference fringe distortion due to the growth strie in the crystal on the beam quality from disk laser and the laser threshold remain to be improved.