Using the nearly centenary precipitation data in Beijing,analysed is the evolution of the different grades precipitation process during summer (June—August) and the relationship between the different grades precipitation process with the dryness and wetness in Beijing. The result showed that correlation between the torrential rain process during summer with drgness and wetnessin Beijing summer was very well,in other words,more or less of the torrential rain process during summer can directly show the dryness and wetness in Beijing. By analysis of the frequency of precipitation process appeared in the dryness years or wetness years,it is shown that the dryness and wetness had less relation to the number of precipitation process in summer,and more relation to the number and intensity of the torrential rain process. So the short range climate forecast of dryness or wetness must be related with the sort range climate forecast of the torrential rain process.