Abstract: A diodepumped Nd:YAG disk laser with high efficiency is reported. A fourpass optical coupling system is well design to obtain a nearly flat top pump profile. An average output power of 101 W is achieved from one single disk with a thickness of 1mm. The average pumping power of the diode laser array is 252W with an electrical to optical efficiency of more than 45%. The optical efficiency of the laser system is 40% and the electrical to optical efficiency is more than 18%.