Abstract: Based on the high-density visibility monitoring data from Chaohu Lake area,the spatial and temporal distribution characteristics of visibility were analyzed,and the influence mechanism of the lake and surrounding topography on visibility and fog formation was preliminarily discussed.The results show that the visibility over Chaohu Lake is lower than that of far shore due to the influence of temperature,wind and water vapor.Generally,fog forms first in the far shore area compared with the nearshore area,but the nearshore area fog lasts for a long time and dissipates slowly.Under the action of lacustrine wind or dominant wind,the occurrence and duration of fog on the north and southwest coast of Chaohu Lake are obviously more than those in other areas.Due to the impact of mountains on the southeast coast of Chaohu Lake,dry and cold mountain winds at night improve the visibility on the shore and reduce the occurrence of fog.