Abstract: In recent years, affected by the global climate change, extreme weather events in frequent situation, extreme, sudden, destructive floods disaster threat, especially the urban basin flood more harmful than general urban floods, post-disaster rainstorm flood investigation and analysis is of great significance, the “23·7” Haihe basin extraordinary flood is the largest basin flood in Beijing since 1963, comprehensively, objectively describe the rainstorm flood process, the causes, development, magnitude of scientific evaluation, for the future Haihe river basin water conservancy planning, engineering construction, flood control and disaster reduction to provide scientific basis. This paper is based on the investigation and evaluation of the “23·7” Haihe basin extraordinary flood in Beijing, comprehensively analyzes the climate background of the rainstorm, the flood process, the characteristics of the “23·7” Haihe basin extraordinary flood , and comparison with the historical rainstorm flood, the research results are informative, reasonable analysis, and the construction of the "three lines", flood control and disaster reduction and promoting the development of river basin water conservancy with high quality will be of great significance.