This paper analyzed the dense fogs with low visibility (<0.5 km) that occurred from June 2012 to June 2014 on the Jiangsu Coast Expressway, and investigated the climate characteristics, meteorological elements and main circulation situation of these dense fogs with low visibility. The results indicated that there are significant differences in the monthly frequency of the dense fogs. Fogs occur frequently from March to June, and also from December to the next February. The frequency of the dense fog in spring and winter is higher than that in summer and autumn. The peak of the low visibility usually appears during 03:00-05:00 BT in the early morning, and dissipates at around 08:00 BT. If the visibility is lower than 0.5 km, the relative humidity increases to 97%, temperature is 0-4℃, wind speed decreases to less than 2 m?s~(-1), and wind direction is between ENE and SSE, then the visibility can further decrease to less than 0.2 km. The statistical analysis of the circulation background based on 150366 samples indicates that the low visibility in the northern and central section of the expressway is closely related to prefrontal fog. This section is located in the forepart of the cold front, and the warm sector exists in the mid-low level part. The low visibility of the whole expressway is due to the advection fog and radiation fog. The radiation fog exists in the downdrafts of upper air, and the weak pressure field or the high pressure moves to the south on the surface. The advection fog is in the region of thermal advection in the mid-low troposphere and behind the high-pressure system entering the sea or at the east side of the inverted trough, while southeast and east winds are blowing on the surface. Before the dense fog (the visibility<0.2 km) comes, there is a large-amplitude oscillation with obvious "trunk-like" fluctuating forepart in terms of the visibility on the Jiangsu Coast Expressway. This feature provides a basis for monitoring and warning of the dense fog with visibility below 0.2 km.