Ciujung River is one of the most strategic river of Banten Province where it serves as natural drainage, water supply, irrigation, flood control and several national highway toward to the main Airport and Harbour should across it. In the same time, one of the highest risk problem could be generated is the breach of Ciujung Bridge on the highway of TangerangMerak. However, there is no previous study discuss about its potential hazard. This paper discuss the flood flow and the dependable flow pattern around Ciujung Bridge based on field observation, secondary data and mathematical model results. The flow pattern will be predicted by using Hecras 6.2 for 2d unsteady flow. The input hydrograph will be determined based on SNI 2415:2016 for a 50-year return period for the flood condition and Q90% for dependable flow condition. The model result is compared to the field data based on the previous observation of extreme flood in 2013. Model prediction of future extreme flood will be done using extreme rainfall of 100 years period. Based on this model result, a potential update of bridge pier that might be used to reduce the risk of the bridge or the river bank failure, could be discussed.