By analyzing the monitoring data of visibility and environment, reanalysis data of NCEP 1°×1° and CFSV2 (0.5°×0.5°), sounding data, and meteorological elements from automatic weather stations, the paper discusses the persistence of fog and haze in Jiangsu Province in January 2013 and the intensifying burst of fog in 13-14 January 2013. The findings are as follows: Firstly, the zonal circulation in the middle high latitude is straight; Jiangsu then lies in the easterly flow at the base of high pressure; the cold high is more northward. This is the weather situation of the persistent fog and haze in January. The weak cold air caused by the weak northward meridional wind provides the favorable conditions. Secondly, the near surface relative humidity is above 85%, wind is eastward and the speed is under 3 m·s-1, and dew point difference is smaller than 3℃. Thirdly, the intensification of the fog is partly triggered by the drastic fall in temperature caused jointly by temperature drop from ground radiation and cold advection. Cold advection near the ground and the warm advection above the mixing layer provide stable atmospheric stratification conditions. The weak upward motion near surface and weak downward motion in middle high level are the dynamic mechanism of the rapid intensification of fog in the early morning of 14 January.