Correlation analysis between point rainfall of every rainfall station and area rainfall has been done based on the historic rainfall data.Then the key rainfall stations can be selected combined with the rainfall stations distribution chart,which are high relativity and region representative.Under the condition of key stations working well,the duration area rainfall can be calculated according to duration rainfall data from the key stations by using the method of fixed point and area,then the flood process can be forecasted.The method doesn't rely on the rainfall data from all the stations in watershed and can effectively solve the problems concerned flood forecasting when it is short of rainfall data.