The aim of this study is to estimate influence of sewerage system on overland flood flow. First, in comparison with the experimental results on water level of overland flood flow due to dam break, the accuracy of numerical model for overland flood flow is evaluated and validity of moving critical depth is found out. Next, numerical simulation for three cases (the case without sewerage system, the case with sewerage system, the case with sewerage system except discharge form pomp) is made, and then the characteristics of numerical simulation model considered with sewerage system for overland flood flow is obtained. In the heavy Flooding like this analysis condition, flood water spurt from manhole. From this study, it is found that numerical modelconsidered with sewerage system for overland flood flow is important to construct of evacuation system.