As an important reference for hydrological work in Jiangsu Province, "84 Atlas" has been widely used in flood control planning and runoff forecasting. However, under the influence of climate change and human activities, "84 Atlas" can no longer meet the social needs under the current conditions. In order to revise the parameters for hilly area of southern Jiangsu in "84 Atlas", this article took the upper basin (Chushanqiao) of Dagang River basin, a typical experimental small watershed, as the study area and conducted a study on runoff generation and concentration regular patterns based on the flood events information. A calculation scheme of runoff generation with optimized parameter was built and different schemes of parameters optimization in runoff concentration was set. The results of flood data from 2020 to 2023 indicated: (1)After parameter optimization, the error of flood runoff depth in 2021 and 2023 is within 25%, the average error of runoff depth is 12.3%, and the calculation accuracy of runoff generation reaches the Grade A standard. (2) The calculation accuracy of concentration has been improved to varying degrees in parameter schemes comparing with the original method in "84 Atlas". The parameter scheme which simultaneously optimize two parameters of instantaneous unit hydrograph has the highest accuracy with an average Nash efficiency coefficient of 0.7 in 2021 and 2023, and qualification rate of flood peak error is 62%. The accuracy of flow concentration reaches the Class C standard. It is concluded that the method of "84 Atlas" with parameter optimization can effectively improve the accuracy of runoff generation and concentration. The results not only provide reference for the revision of the "84 Atlas" in Jiangsu Province, but also have guiding significance for the study of runoff generation and concentration of small watersheds in hilly areas.