Abstract: The performance of the optical parametric oscillator was reported, which was based on the non-critical phase matching of the arsenic acid potassium titanium oxide (RTP) crystal. The intra-cavity RTP-OPO system was driven by the LD end pumped Nd:YAP laser. The output characteristics of the signal light were compared at the different pulse repetition rates of the acousto-optic Q-switcher. The 1.65 m eye-safety laser was obtained when the incident diode pump power of 13.1 W and the pulse repetition frequency of 20 kHz, the maximum average output power was up to 1.1 W and which was achieved with the conversion efficiency of 8.4%. The shortest pulse width of 4.4 ns and the highest peak power of 30.8 kW were obtained when the pulse repetition rate was 5 kHz. The results show that the RTP crystal with the OPO frequency conversion system is a new way to get 1.6 m wavelength laser.