As a complex system engineering, population risk assessment for rainstorm flood disaster has a very important significance on the theory and practice of flood control. Targeting on the problem that dynamic changes of population risk for rainstorm flood should be obtained by disaster management, this paper constructs population risk assessment model for rainstorm flood by using agent-based modeling (ABM) method. On NetLogo platform, agent-based simulation (ABS) and the constructed model are employed to simulate the population risk changes for rainstorm of the Huaihe River Basin. The simulation results show that the proposed model can dynamically analyze population risk under low-risk status, medium-risk status and high-risk status. The experimental results demonstrate that the dynamic changes of population risk in the whole process of rainstorm flood could be solved by using ABM and ABS.