Abstract: In this paper, a case study of the process of a severe rain storm in North China by two meso–αvortices has been made. It is found that the heavy rain has been caused by the interaction between a meso–αvortex coming from northwestern China and a meso–αvortex from southwestern China located in the same longtitude. It is also found that the inertic gravitational wave instability and condition symmetric instability may have a contribution to the suddenly heavy rainfall in the north of north China plain