Based on the daily observation data and numerical forecast products，two typical severe cold wave processes during 2-4 and 20-21， December 2008 have been analy ze d， utilizing synoptic and diagnostic analyses and the forecasting result from t h e cold wave forecasting system of Ningxia．The results showed that, based on the warming strongly before the twice cold wave，strong cold air was accumulated in West Siberia and Baikal Lake and broke out southward； the circulation pattern s showed a trough and a ridge at middle and high latitudes in Asia, dynamic mechanisms were an upper rotating lowpressure trough and strong front zo ne， and the stream fields leading to outbreak of cold wave were the low trough rotating patt ern during twice cold wave； after the outbreak of cold air， strong cold advection controlled Ningxia and co ld high pressure entered into the key areas and reached cold wave intensity. How ever because of the differences of circulation background, the weather impact sy stem as well as the intensity, development and moving path of cold air currents, the cooling range and the impact on Ningxia of the two cold wave processes were different． The main forecast factors of winter cold wave in Ningxia were put f orward based on the above analyses. Based on the daily observation data and numerical forecast products，two typical severe cold wave processes during 2-4 and 20-21， December 2008 have been analy ze d， utilizing synoptic and diagnostic analyses and the forecasting result from t h e cold wave forecasting system of Ningxia．The results showed that, based on the warming strongly before the twice cold wave，strong cold air was accumulated in West Siberia and Baikal Lake and broke out southward； the circulation pattern s showed a trough and a ridge at middle and high latitudes in Asia, dynamic mechanisms were an upper rotating lowpressure trough and