The invention discloses a device for accurately discarding and separating urban initial rainwater, comprising a rainwater inlet and a collection opening, wherein the rainwater inlet is formed in an upper part of the device, the collection opening is formed in a middle part of the device, a baffle plate is also arranged inside the device, the top end of the baffle plate is arranged below the collection opening, the bottom of the baffle plate is arranged at a bottom surface in the device, a chamber that is formed by a side wall where the baffle plate is arranged and a side wall where the collection opening is formed is divided into an upper chamber and a lower chamber by a separating plate, a drain hole is formed in the separating plate, a rainwater discarding plate is transversely arranged at a lower part of the baffle plate, and divides a chamber that is formed by opposite side walls of the baffle plate and the collection opening into an upper rainwater accumulating chamber and a lower rainwater discarding chamber, the rainwater discarding chamber is externally connected to a rainwater discarding pipe, a rainwater discarding opening is formed in the rainwater discarding plate, and a valve device is arranged in the device, and is configured to control the opening/closing of the rainwater discarding opening and the drain hole. The device according to the invention has the beneficial effects: the automatic and accurate discarding of initial rainwater and the automatic collection of posterior rainwater can be realized at any place in any amount of rainfall, rainwater can be separated effectively to prevent a pipeline from flowing backward, flood draining safety is ensured, and the device is convenient to repair and maintain.