The reasoning formula,as widely used at home,is a simplified method of calculating storms and floods of small watersheds.The reasoning formula of Jiangxi Province applied five-point-bend and polygonal process line to generalize the forming process of floods,which makes the time coordinate and the time of rainstorms independent of one another.When calculating the composition of regional floods,because of the independent time coordinate of each regional flood,they cannot be directly added,but must first be unified.According to the relationship between rainfalls and floods of the reasoning formula,this paper put forward a simple method for the reference fo hydrological designers,which postualtes that the time coordinates of floods could be unified to those of rainfall in accordance with the time when flood peaks come.