Abstract: The extracavity-doubling experiment of Nd: YAG ns laser was performed using LBO crystal. In the experiment, the type-I noncritical phase-matched (NCPM) LBO crystal was used with temperature tuned. Through the comparison between the theory of frequency-doubling conversion efficiency and temperature tuning and the experimental data, the experimental results are shown consistent to the theory. When the power of fundamental frequency laser is 1.3 J, the output 532 nm frequency-doubling green laser with the power of 840 mJ is obtained. The highest conversion efficiency is up to 65%. The energy instability of frequency-doubling is less than ±3%.