Abstract: The popularity of smart grids and the edge computing make the traditional network boundary system inadequate in defense, and a large number of terminals involved in the system increases the exposure. The "cloud-edge-end" architecture and the zero-trust engine are proposed for power distribution IoT. Based on SM9, a smart terminal authentication process was illustrated, and a trust assessment approach for smart terminals was proposed with the time degradation factor, the anomalous behavior penalty factor and the authentication factor. The trust value of IoT terminals was calculated through information entropy weighting, which could be applied to the dynamic evaluation of access control. The experiments demonstrate that the proposed authentication and trust assessment scheme can effectively implement the trust assessment, identify abnormal terminal behavior and strengthen the security of authentication of distribution IoT terminals.