In distributed Internet of Things (IoT) systems, nodes store sensitive or important data. Sensitive data is protected through encryption, making key management a crucial concern. In dynamic distributed IoT systems, threshold key management is an effective method for key management. It makes the system scalable and addresses the issue of single-point failures. Moreover, threshold key management can also be applied to message signatures. However, all of these aspects require considerations for identity authentication during node interactions, the security and integrity of data transmission, and the security concerns arising from dynamic changes of nodes in the system. In this paper, we propose a novel threshold key management scheme, which is suitable for dynamic distributed systems. Based on this key management system and a practical distributed communication framework, we also propose a threshold signature protocol that achieves state-of-the-art efficiency based on the above key management system and a practical distributed communication framework. Through security proof, we demonstrate that our system is secure and resilient against collusion attacks and signature forgery. As a type of distributed dynamic network, the keys in blockchain nodes can also adopt our key management scheme to enhance their security. Besides, blockchain can be introduced into our scheme to enhance data integrity.