Adjust-free resonator is applied in the Cr4+:YAG passive Q switched ΟΡΟ laser. Overall performance of laser is much better than that in plane-parallel resonator the wall-plug efficiency rises from 2.2%o to 2.7%o, the 1.57 μm pulse energy rises from 18 mJ to 21.4 mJ, the pulse width decreases from 24 ns to 7.8 ns, the beam divergence decreases from 8 mrad to 7 mrad. Also, the stability of the directional prism resonator's output pulse energy, beam direction, pulse width and wave sh叩e are much better than that of the plane parallel resonator's. After optimization, a smart ΟΡΟ laser with small, nigh efficiency, high stability and high beam quality is obtained.