A software-defined network （SDN） widely used in hospitals is difficult to deal with internal network threats. A Bayesian-based trust management mechanism is designed to identify possible malicious devices inside the network. The mechanism mainly uses the Bayesian inference method to derive the probability of sending malicious attack packets to realize the trust management of the internal devices of the network. Experiments in the simulation environment and the real network environment prove that the method can reduce the trust value of malicious devices faster than similar methods..