Distributed protection is an important research direction for active distribution network with high permeability distributed generation. This paper proposes a distributed intelligent backup protection scheme. And this scheme uses dynamic thresholds to form the start-up criterion of backup protection without the need for complex delay setting. The backup protections at each ring network node can effectively locate the fault section and determine the action smartly with coordination, with the help of the information exchange with its neighbors. The proposed backup protection can provide effective protection under various abnormal conditions, such as communication failure, smart unit failure, breaker miss-tripping and so on. The performance effectiveness of backup protection is verified by the failure simulation examples of active distribution network