The paper selects the daily real observed data over the area between 30-50°N,and 100-120°E from May to September 1998—2004,separates 0800 and 2000BST streamline fields at 500hPa and 700hPa levels into the smooth and separated streamline fields.The result show that mesoscale systems which are blurred in the original streamline fields are clearly discernible in the separated streamline fields.Then,based on the analyses of the movement,evolution and weather character of those mesoscale systems,this paper summarizes main mesoscale systems producing Datong’s convective strong precipitation and heavy rain,and builds prediction models for convective strong precipitation and heavy rain,thus providing some evidence for Datong’s weather prediction.