Research Conclusions: Based upon Gray Theory and Analytic Hierarchy Process, a bridge is divided into three subsystems, namely superstructure, load-transmitted structure and substructure. According to the results measured from the bridge and the specialist's experience, quantitative values of indicating the health state for components can be conducted. The health state of each subsystem is assessed in accordance with that of the components. On the grounds of these, the health state of bridge structure can be produced.