Flood is one of the major disasters in China; while urban flood is the important factor that affect a district in politics and economy. River training works and upstream reservoir regulation are used to control flood in city, which protect people against flood disasters, change the relationship of river channel and subject it to climate change, leading to the variations of the formation and the law of urban flood, and affects the river flood control ability. In this study, inconsistent hydrological frequency analysis theory under changing environment and jump analysis method were used to calculate the flood frequency distribution of Xuan'en county under changing environments; and the flood control ability of Xuan'en station in Zhongjian river was analyzed according to the stage-discharge relation curve of it. The results show that: (1) Average annual maximum monthly rainfall series jumped downward a moderate variation, which indicated that rainfall was decreasing under the changing environment. Annual maximum daily flow series jumped a downward moderate variation, which indicated that flow was decreasing, affected by the influence of climate change and human activities. (2) Consideration of the 0.5 m safe superelevation, the flood control ability of Xuan'en station was less than 10 a at present, which has been of a markedly higher ability than before, but still was not meet the requirements of 20 a flood control planning; and fortification elevation should be raised above 499.29 m. (3) Xuan'en urban river was strongly affected by the river training works; thereby the flood warning plan needs to adapt to the changing environment.