Abstract: Facing the new situations and challenges of hazard weather, the construction of rainfall radar is required to improve the defense ability against rainstorm and flash floods.Described the shortcomings of gauge stations in traditional application, and the methods of rainfall radar quantitative precipitation estimation.In the focused areas, the smaller blind of rainfall radar at 0 °elevation the better to max the coverage range of rainfall radar surveillance.The rainfall radar can move forward the early warning timeline of rainstorm, and improves the identification areas of flash foods, both are effectively; and has ability of switching the passive to active warning before the rainstorm and flash floods happen.The rainfall radar advanced the flash flood warning time by twenty-five minutes of the peak floods which flood flow simulated, but the simulated peaks was lower compared to the real-time measured.In the future, the deeper application of combine rainfall radar with meteorological satellites, ground hydrological station networks, and hydrological monitoring platforms will bring more benefits to rainstorm and flash flood warning, reduction, and relief work.