Trusted Network Connection (TNC) model is applied to ensure the security of network access, and with its deeper research and application, the security of TNC model is very important. First, the paper analyzes the traditional TNC model and its procedure, and finds that there is security risk in the traditional TNC model because of the lack of security in its underlying transport protocol. Then, in order to solve the security risk, the paper designs TNC model and its protocol based on network coding, and improves the trustworthy of network without decreasing the efficiency of data transporting, improves the trustworthy of TNC model.