The dislocation of distribution and density in six crystal rods were determined by birefringence topography and chemical etching. Their optical quality were also inspected by optical method. Laser measurement of output performances of these crystal were conducted in a Q,-switched YAG laser device. The experiment result is shown that the dislocations can form stress field causing strong birefringence when the dislocation density increases to considerable extent. As a result, light wavefront passing through the crystal is distorted and the interference fringes areincreased. As well as extinction ratio in region of high dislocation density is also decreased. Therefore, the dislocation structural defect will also be origin of optical inhomogeneity in crystals. By experimental results of laser performance of these crystal, it is pointed out that there are great influence of dislocation on laser output characteristics. From laser near-field patterns, the laser oscillation can not take place in the region of high dislocation density due to high laser threshold and the light is depolarized by birefringence effect. Because of high dislocation density, the laser divergence is increased and the frequency doubling efficiency is also decreased. The laser output performances changed more obviously when existing decorated dislocations in these crystals.