The methods to calculate the river valley area rainfalls, such as Thiessen polygon method and successive correction method are introduced, and actual area rainfalls of five small valley areas in Hunan in 1998(May-Sep.),1999(May-Sep.) and 2000(May-Aug.) are respectively computed by these methods and arithmetical average method.As a whole, there is not notable difference,but there is a great diversity of area rainfalls day by day using different methods.