The warmarea rainstorm has always been a difficult point in operational forecasting, and forecasting the rainstorm in the double rain belt is even more difficult. There was a severe double belt rainstorm from 20:00 BT 19 to 20:00 BT 20 April 2016, which was missing in forecasting. In order to provide lessons for future forecasts, based on the numerical forecast products, NCEP 1°×1 ° global objective analysis data, conventional meteorological data, the severe double rain belt were analyzed. The results are as follows. The predicted 500 hPa trough was far from Yulin, the convergence line at 925 hPa was not obvious, and the rainfall was small. The effect of cooling trough in front of the south branch trough was neglected. The cold air was misjudged into the sea, and the effect of backflow on Yulin was ignored. The CAPE value was not analyzed in detail and it was not found that before the rainstorm Yulin had favorable dynamic conditions for “dry and wet”, which was easy to trigger rainstorm. The energy frontogenesis contributed to the rise of convective instability. The lowlevel jet provided a continuous flow of water vapor for the south rain belt and the large area of water vapor flux and the convergence area of water vapor are concentrated in Yulin, which is conducive to the occurrence and development of rainstorms.