The effect of the East Asian jet stream on the freezing rain and snowstorm over southern China in early 2008 was investigated using the European Centre for Medium-Range Weather Forecasts (ECMWF) interim data and the precipitation data provided by the China Meteorological Administration. Possible reasons for the change of the jet stream during the event were studied. The variation of the vertical motion in the jet entrance region was caused by changes in the intensity and position of the jet stream, leading to the development of precipitation over southern China. In order to study the causes of changes in the jet stream during the event, the eddy kinetic energy equation was used in this study. The analysis suggests that the development of the jet stream was corresponding to the variation of the eddy kinetic energy. The eddy geopotential advection made an important contribution to the eddy kinetic energy. A small eddy kinetic energy center associated with weak wind fields was located to the north of the jet stream, and the eddy kinetic energy was transported via the eddy geopotential flux to the jet entrance region and converged there, leading to the intensification of the jet stream.