Abstract: With the development of the interconnection of all things(IoT), a large number of mobile terminal devices with multiple users access the distribution network, and gradually form an open and interconnected network environment, which brings new challenges to the security and protection of the distribution network. In this paper, a method of analyzing the sensing data of the digital substation is proposed, which can prevent the abnormal data from causing the malfunction of the relay protection switch by calculating the creditability of the sensing data. Big data based creditability calculation , and the implementation of the intrusion tolerance algorithm are studied throughout the paper. The simulation results show that the proposed creditability-based intrusion-tolerant(CIT) algorithm can ensure that the protection equipments have no protection malfunction from the false data attacks or the physical damage attacks(on PE‘s hardware modules), and the proposed intrusion tolerant algorithm has little affect on the real-time performance of the original relay protection algorithm, hence it has some practical value.