Abstract: An underwater low-light-level imaging system for anti-terrorism operation is introduced, and its key techniques are addressed. According to the optical characteristics of ocean water and low-light-level imaging environment, a dedicated underwater lens was designed, which can correct the aberration and overcome the influence of water medium. The finite element analysis was made for the sealed cabin of its detectors to ensure its reliability and make the mechanic design simple. The system was successfully demonstrated in Qingdao sailing boat game. The test results show that the system works reliably under the water pressure of 300 meters, its imaging quality is high and it can provide time critical warning for dangerous item.