Abstract: By employing conventional observation data, NCEP/NCAR 1°×1°reanalysis data, as well as FY-2E water vapor images, the characteristics of cold air intrusion during a typhoon-related torrential rain event in Shandong Peninsula is analyzed. Results reveal that the typhoon, moving northward and being coalesced with continental polar air, was a major contributing factor to the torrential rain. The cold and dry air intruded into the typhoon circulation from the west side, induced baroclinic frontogenesis and extratropical transition of typhoon, and resulted in transition from baroclinic potential energy to kinetic energy and the strengthening of the ascending motion. The cold air was characterized by high potential vorticity and low humidity. Dark zones in water vapor satellite imageries corresponded well with the areas of low humidity and high potential vorticity in high isentropic surface. Satellite imagery in the water vapor channel directly demonstrated the process of system evolution. The combination of typhoon circulation and baroclinic leaf was firstly developed into a new vortex and then a comma cloud. Water vapor dark zones associated with cold and dry air constantly developed from dry tongue to dry slot, which was drawn into the center of the vortex. Besides the identification of flow pattern, by analyzing water vapor images, the characteristics of dry or moist zone and their boundaries can also be clearly identified. Comparison analysis of continuous water vapor images provides the forecaster with additional information on dynamic properties in high levels, which is especially helpful when issuing severe weather warnings.