By use of the meso-scale non-hydrostatic model MM5(V3),and the observational data and T213 output data,we simulate and analyze the backflow precipitation over North China on Dec.22—23,2002.The results show that the lower level Northeast airflow was dry and cold,and it acted as a cold wedge;the start and end time of precipitation were closely correlated to the wind direction,including the upper warm air flow and lower cold air flow;and the precipitation strength was correlated to the wind speed.The moisture came from the South along with the south-west air flow.