The invention discloses a rainwater discarding device, comprising a silt shaft and a discarder; the discarder is placed in the silt shaft; the silt shaft comprises an upstream pipeline socket, a downstream pipeline socket and a discharging opening; the discarder comprises a stainless steel round bucket, and the inner part is provided with a float ball, the stainless steel round bucket and a stainless steel discharge bending pipe and other components. The rainwater discarding device is simple in structure can shunt rainwater while accurately control the initial rainwater flow, improve the rainwater utilization rate; the rainwater with good quality at later period can be retained and collected, and the initial rainwater is discarded effectively; moreover, the device is low in cost, and suitable for different rainfall features, and good for popularization and application.