Abstract: In order to improve the security of SDH equipments, a new kind of security modeling method based on Bayesian network is proposed. According to the relationship of four factors of information security, the threaten and vulnerability of SDH equipments in power communication network are analyzed in the view of information and physical fusion, and the comprehensive security evaluation model of SDH equipments is built based on Bayesian network. In this paper, by taking SDH equipment in power communication network of a power supply company as example, the influence of each defense measure on the security of the equipment is analyzed. Through the comparison and analysis of results, the practicality and accuracy of proposed mode are verified. And the evaluation results obtained by this method can help decision-maker for selecting effective defense measures to improve the security of equipment.