With the Nd∶YAG transparent ceramics as the gain media, a laser property evaluation system is built. The effect of the Nd∶YAG transparent ceramic size on the laser property is studied. The experimental results show that, when the Nd∶YAG transparent ceramic size is relatively small, the laser output power increases with the increase of the size under the same pump power, but the increase amplitude declines. When the Nd∶YAG transparent ceramic size is 3 mm×3 mm×9 mm, the continuous laser output with a power of 4.94 W and a corresponding slope efficiency of 37.7% is obtained. When the pump power is 17 W, the numerical simulation results on the variation of the laser output power with the Nd∶YAG transparent ceramic size is consistent with the experimental results. Compared with the Nd∶YAG monocrystal, the Nd∶YAG transparent ceramics can be used to improve laser properties if its doping concentration is enhanced.