According to the application of underwater target detection, the corresponding 532 nm wavelength lidar system parameters were given. Combining the advantages of streak tube lidar and subcarrier modulated lidar, a prototype of underwater 3D imaging extended range lidar was designed. Compared with the common scheme of microwave modulated laser to generate high frequency pulse, the prototype adopted Q-switch technology to compress laser pulse, and then combined the characteristics of F-P cavity to generate high frequency laser pulse, which had the advantages of high peak power and high output energy. The experimental results show that the imaging distance of the prototype in clear water environment is better than 20 m, and it can capture the target details with a diameter of 9 mm at 13 m. In the turbid water environment, the range-extended capability of signal processing is 81.4%, and the range resolution error is 0.01 m. The experimental results provide a foundation for further improving the imaging range and resolution of underwater lidar and developing underwater imaging equipment.