Statistical data from the Center for Research on the Epidemiology of Disasters show that flood disasters occurred frequently and affect a lot of residents. Therefore, risk management plays an important role. In risk management, the flood damage assessment is the basis of risk analysis which is the first work. This research focuses on the ways of flood damage assessment and considers uncertainty to build the methodology of flood damage assessment. Finally, this study estimates the risk of residential area. At present, there are many ways to estimate flood damage, and flood depth damage curve is the most common one. The curve can be constructed in two ways, Questionnaire and Synthesis. Because questionnaire costs a lot of manpower and money and is restricted to having history flood damage data, the method of synthesis is applied in this research. This method considers uncertainty which was not included traditionally. The Shi-Ju City in Taipei Metropolitan was used as a demonstration area for this study. First, this research analyzes the declaration data for individual damage in disaster of National Tax Administration and the Na-Li typhoon damage data. Then the loss density functions of each facility and the damage probability of each depth will be estimated. Secondly, Monte Carlo simulation will be used to determine the probability distribution of damage under a specific flood depth. Thirdly, the probabilistic model will be applied to establish the damage-depth curve under different exceeding probabilities. Finally, the result will be applied to estimate the average annual damage of residential area. The results show that average annual damage is a probability density function. The way of considering uncertainty in this research is more flexible than the traditional way is when being applied to risk management.