Flood Risk Identification and Resilience Building Strategies for Mountainous County Level City—A Case Study of Xichuan

China has a large number of county-level cities in mountainous areas which are very prone to rainstorm-caused floods. Moreover, as county-level city, the exposures, as well as available funding and technologies, are very limited, and flood control standards are also constrained, therefore, resilience building is essential for flood management. Taking Xichuan as an example, this paper performed the analysis on the present, future, and residual flood risks in the urban area using flood simulation and scenario analysis methods, in which several key factors were taken into account, including built-up area expansion, flood control infrastructure improvement, rainfall change due to climate warming, and changes in the hydrological characteristics of the underlying surface due to human activities. Based on these findings, the strategies were proposed and analyzed for resilience building, including (1) practicing systematic management at river basin scale to delay and cut down of peak discharge flow of floods to the city, (2) establishing a multi-level, synergistic defense system integrating gray, green, and blue infrastructures to mitigate flooding, waterlogging and river bank erosion in urban areas, (3) enhancing the resilience of key infrastructures to keep the basic functions for the city during flooding, (4) strengthening monitoring and early warning capabilities, and (5) raising public’s awareness of flood risks and capacity of responding to floods, both (4) and (5) are significantly helpful for the public to timely take correct actions in case of floods.