Based on the principle of transient disturbance analysis, a method is provided to objectively determine the weather pattern owing to the sea fog. On the basis of classification results, a synthetic analysis is conducted of the circulation situation, divergence, vertical velocity field, and the vertical profiles of temperature and humidity. The basic characteristics of the circulation and physical field of the sea fog (L type sea fog) under low pressure control at 1 000 hPa are obtained, which are compared with those of the sea fog (H type sea fog) under high pressure control. The results are as follows: 1) The negative anomaly disturbance of L type sea fog's geopotential height is mainly manifested at the low layer, whose average value is -65.66 gpm, and is gradually weakened upward; 2) When L type sea fog occurs, its temperature inversion structure is weaker than that of H type sea fog, the layer is thicker, and the upper layer has higher relative humidity, while the upper layer of H type sea fog is relatively dry; 3) L type sea fog has a structure of three layers at the vertical direction. The first layer is convergence accompanied by weak ascending and sinking motion from 1 000 hPa to 950 hPa, the second layer is divergence accompanied by weak sinking motion from 950 hPa to 850 hPa, and the third layer has gradually strengthened ascending motion from 850 hPa to 500 hPa. However, H type sea fog has a structure of two layers. It is divergence accompanied by weak ascending and sinking motion at 1 000 hPa and has consistent sinking motion from 950 hPa to 500 hPa. 4) The statistical analysis of probability density further quantitatively show the vertical movement of L and H type sea fog and the distribution of relative humidity at each layer. These conclusions provide an important reference for forecasting the sea fog over the northwestern Yellow Sea under low pressure circulation in summer.