The invention discloses an underwater laser line scanning digital imaging system which comprises an upper computer module (8), a cylindrical pressure resistant shell (9), a laser module (1), an optical-mechanical-electrical scanning module and a digitization camera shooting module, wherein the laser module (1), the optical-mechanical-electrical scanning module and the digitization camera shooting module are installed inside the shell (9). The laser module (1) comprises a solid-state frequency doubling laser device, an optical focusing system and a laser control system. The optical-mechanical-electrical scanning module comprises an input reflecting mirror (2), an optical subsystem (3) and an output reflecting mirror (4), wherein the optical subsystem (3) comprises an optical trigger, a motor and a rotary shaft driven by the motor. The digitization camera shooting module comprises an incident hole (5), a receiving machine (6), a low-noise pre-amplifier and a video processing system (7). The upper computer module (8) comprises a keyboard, a mouse and a video monitor. According to the underwater laser line scanning digital imaging system, back scattering influences in absorption and scanning water space can be reduced to the maximum degree, and a high-resolution image can be provided.