The interaction between nodes to achieve service in Cloud computing is allowed. In the complex and dynamic network environment, access control and security communications are the main ways to protect the security. It provides a trust dynamic level access control method by simulating social trust, which can help users select a trustworthy node in internet. The comprehensive trust model is composed of direct trust and indirect trust. The direct trust value is deduced from user’s satisfaction with interaction, amount of interactions, time decay, and punishment factor. The indirect trust is computed by direct trust in other nodes for the feature of trust transference. The trust dynamic access method will help users to select more secure service and provide reliable candidate nodes. The experiments show that trust mechanism can improve the credibility of the system in a certain extent and reduce deception task execution. The method can improve the efficiency of interaction, and is suitable for cloud computing environments.