Abstract:In terms of observed data and NCEP reanalyzed data, circulation background and d ry cold activity features of the persistent snowfall in Shandong Peninsula duri ng December of 2005 were analyzed. The roles of dry cold air in this event were researched by using the moist potential vorticity and frontogenesis theories. T he results suggested that the change of snowfall in Shandong Peninsula could be well reflected by the low level humidity field, while it was closely associated with upper level dry cold air. The upper troposphere potential vorticity are a was corresponded with the low relative humidity area. Dry air came mainly from the northern part (high latitude) of upper troposphere. The down and sou th stretching of potential vorticity area and low humidity area were correspond ed with the low level moist symmetry instability area. The severe snowfall occurred under the common actions of the lifting of topographic and frontogenesis forcin g of low level saturation moist air, as well as the releasing of moist symmetry instability energy. The incursion of dry cold air was the trigger mechanism of the releasing of instability energy.