Water conservancy project is one of the most important factors of the impacts from human activities on the flood. With the large-scale construction of water conservancy engineering projects all over the country in recent years, its effects become more obvious and vary for different types of flood in different regions. In this paper, the basic operation data of large, medium, and small water conservancy projects in the upstream of Fengman of the second Songhua River Basin were analyzed. Based on the flood classification of “Standard of Hydrology Information Forecast”, the impact rules between water conservancy projects and different types of floods were determined by the statistical method, and they were converted into the impact parameters of water conservancy projects. These parameters were added into the Xinanjiang model of flood simulation, and the impact degrees of water conservancy projects on different types of flood were then obtained in consideration of the requirement of prediction precision. The research can provide a new idea for study the impacts of human activities on flood.