The present invention provides a method for forwarding a protocol frame in spanning rings, applied to the Ethernet ring network including a crossed or tangent ring and sub-ring. The method comprises steps as follows: when an interconnection node of the ring and the sub-ring receives a protocol frame from a sub-ring, if the topology of the sub-ring is changed, the interconnection node updates its address forwarding table according to the address updating information carried in the protocol frame, and sends the address updating information to the ring; the nodes of the ring update their address forwarding table respectively according the updating information. The present invention selectively sends information of sub-ring protocol frame to the ring via the interconnection node of the ring and the sub-ring. Such scheme that information of the sub-ring protocol frame is selective sent at the interconnection node not only solves the problem of updating address in spanning rings, but also decreases the amount of protocol frames sent from the sub-ring to the ring, and thereby greatly improves the performance and efficiency of the network.