A diode array side pumped Nd:YAG thin disk laser was reported, and the light distribution of doped crystal and temperature distribution of the radial were studied theoretically and experimentally. The output laser peak power of 230 W, opt.-opt. efficiency of 33.5% and beam parameter product of 21.6 mm·mrad were obtained. The results of experiment showed that side pumped Nd:YAG thin disk laser could realize light uniform distribution, and decrease temperature difference of radial significantly. And composited Nd:YAG/YAG cryatal could satisfy the requirements of side pumped thin disk laser. These techniques and methods could apply to higher power side pumped thin disk laser.