In the Internet of things (IoT) cloud platform, the data is collected and used by the nodes of IoT, and the processing and storage of data is based on the cloud platform. The platform has increased the data processing and sharing abilities of IoT, meanwhile, it also has enriched the resource in cloud and improved integration of the Internet and human world. All of this offers advantage as well as new problems of information security. As the characteristic and limitation of the nodes of IoT, they are particularly vulnerable, thus it is a crucial and urgent issue that how to realize the trusted update of authorization for the hijacked nodes . In order to solve this problem, we propose a PRE based trusted update scheme of authorization for nodes on IoT cloud platform (PRE-TUAN). At first, we define the system model including the trusted IoT data server and permission management server, and the semi-trusted proxy re-encryption server in cloud. Secondly, describe the system processing and algorithms. Finally, analyze and prove the security of PRE-TUAN. PRE-TUAN is based on the proxy re-encryption (PRE), which will reach the full potential of cloud computing, and ensure the security and reliability of the data in IoT cloud.