In order to estimate the carbon footprint of bridge during whole life cycle, a quantitative model is established in this paper. The life cycle is divided into five phases as design, manufacturing, construction, operation & maintenance and demolishing. According to energy and resource consumption, the carbon footprint of different source, such as material, transportation, construction, facility etc, is accounted according to the criterion of mass and cost. The carbon intensity index is proposed considering the feature of bridge engineering and economic cost. A multi-level assessment method is developed based on modified analytic hierarchy process and comprehensive variable weight analysis. As a case study, south lake bridge in Wuhan is analyzed, the assessment results indicate that the carbon intensity of this bridge is between small and moderate, and the carbon footprint is mainly concentrated in the phases of manufacturing and construction. The carbon footprint model and carbon intensity index assessment method which combine environmental impact together with economic cost, are of high applicability in real bridge project, and could be used as a reference for bridge management section to assess the life cycle environmental impact.