At present, a large number of independent Internet of Things (IoT) systems are constructed, resulting in the phenomenon of data islands. In the future, the IoT will urgently require efficient collaboration between independent IoT terminals and systems to meet the increasing and diversified IoT needs. However, in the process of the integration of blockchain and identity authentication mechanism, there are problems such as difficult unification of cross-domain identity trust mapping and low efficiency of authentication service. A cross-domain identity trust authentication scheme for the IoT is proposed by us. We integrate edge computing and blockchain, introduce side chain technology to construct master-slave chain, propose and improve Identity-Based Cryptograph (IBC) mechanism under cross-domain trusted architecture, and design cross-domain trusted authentication architecture. The analysis and evaluation show that this scheme implements the trusted mapping between data on the blockchain, improves the efficiency of cross-domain terminal authentication.