To study the impact of population dynamic changes on the life loss risk in rainstorm and flood disasters, a precise assessment of the population life loss risk in flood disasters was conducted from a dynamic perspective. By defining the concept and characteristics of population life loss risk and analyzing its influencing factors in flood disaster scenarios, a framework for assessing the population life loss risk in rainstorm and flood disasters was established. A dynamic assessment model of population life loss risk was constructed using multi-agent modeling, simulation technology, and one- and two- dimensional coupled MIKE model, and applied to the main urban area of Nanjing City. The results show that a longer rainstorm return period leads to a higher population life loss risk, the number of people exposed outdoors increases first and then decreases during the rainfall process, and the population life loss risk increases first and then decreases slowly. The assessment model can dynamically calculate the population life loss risk due to flood disasters and illustrate the changes in population distribution and evolution process of the population life loss risk under different flood disaster scenarios. Keywords: flood disaster; population life loss risk; multi-agent modeling; one- and two-dimensional coupled MIKE model; Nanjing