Using the hourly precipitation data,surface wind filed,upper air data and radar echo data in Hunan province from 13 to 14 June in 1998, the evolution character of the mesoscale proess was analysed preliminarily.The mesoscale system——direct cause of the heavy rain and the corresponding connection for heavy rain with physical quantity,active of mesolow circulation were pointed out.The large scale circulation situation, mesoscale convergence line and orographic action provided advantage condition for local large heavy rain.