Rainwater drainage system of building

The utility model discloses a rainwater drainage system of a building, which comprises a drainage ditch and drainage main pipes, the drainage ditch is arranged on a top platform of the building, the drainage ditch is arranged in a circle along the edge of the top platform of the building, a rainwater filtering and draining device is arranged in the drainage ditch, and the drainage main pipes are fixedly arranged on an outer wall of the building. The rainwater filtering and discharging device is of a segmented connection structure and has the advantages of being convenient to lay and easy to take out and clean, the filtering and discharging groove is divided into the upper layer and the lower layer, sundries in rainwater can be filtered out, and the rainwater filtering and discharging device is convenient to clean. According to the utility model, a pipe crack warning structure is further designed, so that a leakage point can be quickly found when the drainage pipe leaks water, and the drainage pipe is convenie