A device for separating light flaky cut rolled stems (CRSs) by a throwing roller is provided. The device includes a vertically provided separation bin, and a CRS guide device and a CRS distribution plate which are arranged in the separation bin. The present disclosure further provides a method for separating light flaky CRSs by using the device. The present disclosure achieves full separation of finished CRSs from light flaky CRSs. The device of the present disclosure is designed for the first time, and can be directly connected to a pneumatic CRS feeding and discharging section of a production line. The device of the present disclosure is compact and suitable for industrial production.