Basic frequency laser of high power operating on the condition of low-ordermode was obtained according to the design of U shape resonant cavity which could get large volume of basic frequency. In the experiment, concave mirror inserted inside the cavity compensating the thermal birefringence to obtain high output powerwas analyzed the oreticallywhich was in good agreement with experimental data. In the experiment, we adop ted 9 LD bars, each of which have 20W output power to side pump single 2mm Nd∶YAG stick, and U shape design to realizeM- factor 1. 8,the output power stability of the laser RMS < 1% and the 22. 3W output power.