According to the rainstorm flood reasoning formula recommended by the Jiangxi Provincial Rainstorm Flood Calculation Manual in 2010,the design peak flow of small wat-ershed is generally solved by the graphical method.Although the Graphic method is easy to understand,but in finding the intersection of two curves are also prone to reading errors,and difficult to use computer language programming.In this paper,according to the current hydrological manual used in the graphical method to optimize its calculation method,making the original curve equations into linear equations,proposed a feasible and easy to imple-ment programming optimization algorithm for hydrological designers.