A risk assessment model based on Bayesian network was proposed.In this model,each risk event influencing the Trusted Platform Control Module(TPCM)'s trust was analyzed.According to the relation among risks,the Bayesian network evaluation model was built.According to the evaluation from expert,Bayesian network inferring method was used to evaluate the risk probability and its influence.The whole system's risk value and risk priority were determined.An example was given to verify the model's correctness and validation.