Flood risk assessment methods are divided into three types including index system-based assessment method, historical flood hazard-based assessment method and simulation-based assessment method and the three types of methods are reviewed respectively. The index system-based assessment method can only be used for rough assessments because its model and parameters are difficult to validate. The historical flood hazard-based assessment method can not be used for flood risk assessments independently in general because its results often require an amendment by simulation analysis and its data requirements are difficult to satisfy. Simulation-based assessment method is based on a clear physical mechanism and has many important advantages. In recent years, some progress has been made on how to deal with the two significant constraints of simulation-based method, i.e. the data availability and the computational complexity. Simulation-based assessment method should give full consideration to the hydraulic interactions between upper-and lower-reaches, in which its research area is the best including an entire catchments. How to obtain a balance among data availability, computational complexity and accuracy and how to carry out verifiable analysis for the assessment results are still the current important problems, which may be the two major directions for the future research.