An IAB node switching method is applied to a relay system, and the relay system includes a donor base station and a first IAB node. The donor base station provides a gateway function for the first IAB node. The first IAB node receives a first BWP configuration from the donor base station, where the first BWP configuration includes a BWP configuration of a second IAB node, and the second IAB node is a candidate upper-level node of the first IAB node. The first IAB node switches to the second IAB node. According to the IAB node switching method, the IAB node, and the donor base station that are provided in this application, service availability of an IAB node is ensured when the IAB node has a plurality of upper-level nodes.