Abstract:By using the weather chart, surface densified observation of precipitation, sounding data and NCEP/NCAR reanalysis data (resolution 1°×1°), the large scale persistent 　　severe precipitation in southern North China from 9 to 10 May 2009 is analyzed. Results demonstrate that the severe precipitation is produced when the cold air met with southwest warm wet air. There is southwest current ahead of the trough at 500 hPa. and the northeast southwest shear line at the 850 and 700 hPa. The surface cold front turns to stationary front. Then the weak cyclonic wave is formed and moved to southeast and finally disappears. The atmosphere has high temperature and humidity. There are weak convective instability and symmetric instability in middle levels. The invasion of cold air takes place in the lower levels. The cold air meets with warm wet air to form the convergence and updraft on the one hand, and on the other hand, the cold air makes the warm wet air ascended. As a result, the ascending movement has been strengthened and the precipitation is increase. The middle high level atmosphere is warm and wet. The level of 0 ℃ is relatively high. The weather mainly is severe precipitation accompanied with thunder and lightning. Owing to the severe warm and wet currents, the cold air weakens during moving to southward and the velocity slows down. The cold air and warm air confront each other for a long time in the lower reaches of the Huanghe River, therefore, the severe precipitation is maintained persistently.