Abstract: Affected by various water conservancy projects, the runoff yield and concentration within the Nanpan River basin have significantly changed.The measured hydrological data of Zhanyi Station and Xiqiao Station on the main stream of Nanpan River was inconsistent.By restoring floods at hydrological stations and comparing the differences between natural and measured floods, the impact of various periods and types of water conservancy projects in the upper reaches of Nanpan River on downstream floods had been determined.Physical meaning of specific itemized survey method were adopted to restore each major influencing factor one by one for flood restoration.The impact of water conservancy engineering construction in the upper reaches of Nanpan River on downstream floods were as below.The Zhanyi Station was affected by the upstream reservoir′s regulation and storage, with a flood reduction range of 30% to 35%.Xiqiao Station was affected by both upstream reservoir regulation and floodplain before river regulation, resulting in a 39.7% reduction in flood peak.Xiqiao Station was mainly affected by the upstream reservoir regulation, with a peak flood reduction of 23.5%.The results of analysis can provide a reference for engineering construction, hydrological forecasting models, joint operation of reservoir groups, and river management.