Abstract: In order to study the performance of an Yb:YAG thin disk laser, a 16-pass pumped micro-channel cooled scheme was adopted. The optimum thickness of the Yb:YAG disk, the thermo-mechanical effect in the disk and the laser performance are analyzed. The 16-pass pumping coupling is achieved in preliminary experiment using an Yb:YAG disk (250m in thickness and 10mm in diameter) with atomic fractional 0.1 doping concentration. The output power of 24.4W was obtained from the laser oscillator when the total pump power was 81.9W. The optical-to-optical conversion efficiency was up to 29.8%. The result shows that the higher conversion efficiency can be achieved in the 16-pass pumped micro-channel cooled Yb:YAG thin disk laser.