Floods and droughts exist in hilly red soil areas of the South China. The flood and drought season division can be used to control the disaster as a scientific base. This paper, based on maximum 1-day and 3-days and total precipitation and streamflow in 10-days, divided the flood and drought season into the period earlier than the flood period (Feb.1-28), early flood period (Mar.1-31), flood period (Apr.1-Jun.30), late flood period (Jul.1-Sep.10) and drought period (Sep.11-Jan.31 next year) in the middle and upper reaches of the Ganjiang River by set pair analysis. The result is closely to traditional one. So the set pair analysis can be applied to integrated water resources management with a relatively complete theoretical base.