Abstract: Based on the theoretic optimized values of intracavity passive confocal unstable resonator, the beam quality of optical parametric oscillator (OPO) laser is tested experimentally. The transmission energy of laser is about 70.6 mJ/pulse and far-field divergence angle is below 5mrad. The possible factors of affecting beam quality are analyzed. The high quality of 1.57 m laser can be obtained through optimized design.