Laser diode pumped optical parametric oscillator (OPO) laser is operated in the orthogonal porro-prism resonator. The 1.57 μm eye-safe laser with high mechanical stability, high thermal stability and high beam quality is obtained base on the KTP typeⅡnon-critical phase-matching. A linear polarized-oscillating condition exists in the resonator, and the field of the pump laser for the OPO can be homogenized. The laser solves the problems such as unstable signal output in the intracavity OPO and optical damage due to the exorbitant intracavity power density. The OPO laser is operated in the heat-conducted half-circular LD arrays pumped Nd:YAG laser, and produces the average pulse energy of 86 mJ at 20 Hz in a 5.4 ns pulse with an optical-to-optical conversion efficiency of 9%, the energy stability of ±2.5％, and the beam divergence of 5 mrad.