Sea fog changes widely and rapidly, and existing Lidar scanning speeds are insufficient to detect such changes. Therefore, we developed a Lidar system with a fast scanning speed and long detection distance. Experimental results show that at high scanning speeds, the maximum correlation between the Lidar's visibility results and those from two forward scattering visibility meters reaches 0.9537, with a minimum relative error less than 15.31%. The results also show that the visibility of the proposed Lidar system has high accuracy when fast scanning. During the tests, the Lidar system successfully captured sea fog many times and closely tracked the changes of sea visibility, which verifies the feasibility and reliability of the developed Lidar system for obtaining visibility measurements and sea fog detection.