Abstract: In order to ensure the sustainable development of social, planning, disaster prevention, monitoring and early warning, emergency response and post disaster assessment are increasingly important for scientific and efficient disaster prevention and mitigation. Strengthening disaster risk management is an important strategy for disaster prevention and mitigation. The mountainous areas in China have been attacked by frequent flash floods which are the weakness of flood management. It is the basic work of flood risk management to obtain the information of flash flood risk and flood inundation of mid-small rivers. Based on this, the regional flash flood risk assessment, technical route, key technology and work content of mid-small rivers inundation analysis are discussed, and the expected results are prospected.