Dr3m is a distributed rainfall runoff model, which takes rainfall as input to calculate the rainstorm runoff through drainage pipeline or natural river. The detailed simulation of the rainstorm runoff period selected by the user is provided. The calculation of soil moisture is carried out every day during the rainstorm period. A watershed can be expressed as slope flow, channel and reservoir section, which together describes the drainage function elements of the basin. This model is usually used to simulate small urban basins. The flow and base flow in soil are not simulated, snow and snow melting are not simulated.