Based on the dry intrusion theory and potential vorticity theorem, by using the water vapor image and NCEP/NCAR 1°×1° reanalysis data, the synoptic and dynamic characteristics of a strong storm surge over the Bohai Sea from 3 to 5 March 2007 are analyzed. The feature and influence of dry intrusion on the Yellow River cyclone are also revealed. The result shows that the storm surge occurred during the adjustment of Eurasia mid and high latitude circulation, the east moving and development of unstable low rough and the rebuilding of EastAsia major trough. Northerly gale induced by strongly developed the Yellow River cyclone forced the surge to sharply bloom. Dry intrusion has features of high PV value. The shape and strength changes of high PV area, with dark zone on water vapor image, have a meaningful prediction to different stages of cyclones. When drycold air currents meet with warmer wet air flow along a inverted “Ω” lapping belt from north to south, the isentropic surface becomes steeper and the stability of atmosphere decreases. Although the downward progress of dry intrusion from high level will lead to warming effect, the cooling effect from the strong cold advection can give birth to decreasing of atmospheric stability. Therefore the high level vortex, corresponding to surface cyclone, has lower temperature than the adjacent areas. As a result, the midlow level cyclonic vorticity is increased, the upward vertical movement is reinforced, and then the surface cyclone is strongly developed.