In IoT with Blockchain, an increasing number of mobile IoT devices are starting to work across various locations, requiring operators connected to these IoT devices to provide roaming services. Due to the differences in the blockchains used by operators, a safe and efficient cross-chain model for IoT device roaming settlement is significant for operators. In this paper, a cross-chain model based on credit hierarchical multi-notary is proposed to connect different blockchains in IoT devices roaming settlement. Firstly, a cross-chain election method by sub-notary group is proposed to solve the problem of “Richer Get Richer” in blockchain with credit scheme and avoid risk of malicious notary nodes. Secondly, a re-election mechanism is used to make the process of cross-chain running properly with the number of IoT devices is increasing rapidly and transaction concurrency. Moreover, a weighted voting system is designed for sub-notary group cross-chain model to reduce the influence of malicious notary nodes. Experimental results demonstrate that the proposed cross-chain model performs better on credit ecology and defending malicious nodes’ influence than the model without sub-notary mechanism.