Based on the demand of ocean detection LiDAR to improve the depth of ocean detection, this study combines a 532 nm single longitudinal mode laser pumped KTP-OPO with seed injection technology to design an optical parametric oscillator that can output 972 nm single longitudinal mode laser, high peak power 486 nm blue laser is obtained through external cavity doubling. When the energy of 532 nm laser is 25 mJ and the repetition rate is 100 Hz, the single pulse energy of 972 nm can reach 6.6 mJ, and the maximum conversion efficiency is 26.4%. After frequency doubling, a 486 nm blue laser pulse with a maximum single pulse energy of 1.58 mJ can be obtained, the maximum doubling frequency efficiency of 23.9%, the corresponding pulse width is 4.5 ns, the peak power can reach 351 kW, the beam quality factors Mx2=3.1 and My2=3.3, and the laser is expected to become the new light source of ocean detection LiDAR.