Based on the rain gauge data from automatic weather stations, conventional observations and NCEP analysis data, the extreme rainstorm that hit Suining City from 30 June to 2 July 2013 and the relationship between the extreme rainstorm and the LLJ evolution are studied primarily. This extrem event was caused by the coupling interaction between plateau and southwest vortexes. The results show that the high level vortex development is strengthened when the coupling interaction occurs between plateau and southwest vortexes, stimulating the generation of rainstorms in Suining City. Jet stream provides unstable energy for the development of high level vortex. Ultra low level jet and low level jet cannot cause a strong rainfall immediately, and sometimes severe rainfall process may occur two hours later. The degree of increase in the low level jet index (I) and the intensity of rainfall have a direct proportional relationship.