Yttrium aluminium garnet (YAG) crystals have applications in optoelectronics, and the defect control of crystal growth is a bottleneck problem to be solved. In this work, the dislocation etch pit morphology and density distribution were investigated in YAG crystal grown by the Czochralski method with and without necking technology, and the YAG crystal samples were polished and etched with phosphoric acid. The dislocation etch pits were photographed by a metalphase microscope. The results show that the dislocation density of YAG crystal is the maximum in the initial shoulder part and the minimum in the cylinder part, as well as a little greater at the end part. The dislocation density in necking end is reduced. In addition, the YAG dislocation etch pit of different crystal directions was analyzed, and the surface energy of each YAG crystal surface was calculated, indicating that the relatively stable plane of YAG etch pit is (110) and (112). Based on the analysis by the stereographic projection, the lattice plane stability of (110) and (112) and their position relation to other lattice planes are the important reasons for the formation of etch pit morphology.