We adopted the technology of virtual confocal unstable resonator with Gaussian2reflectivity mirrors which was used to improve the brightness of output beam from solid2state laser to improve the beam quality of OPO. Eigen mode2fields of virtual confocal unstable resonator with Gaussian2reflectivity mirrors was calculated. The pump laser is1. 064μm Nd∶YAG laser and non2critically phase2matched KTP2OPO acted as a single resonator for the signal wave.The highest output single of 60mJ / pluse at 1Hz is obtained with M2 < 3 and conversion efficiency up to 40 %.