Abstract: In order to accurately and quantitatively calculate and assess the carbon dioxide emission during the construction phases of highway tunnels and ascertain the main sources of carbon emission and their influencing mechanisms, a standard calculation process, based on the life cycle assessment (LCA) method, is devised that covers the aspects including highway tunnel carbon emission calculation boundary, list analysis and calculation model creation. By using engineering examples and the life cycle assessment tool SimaPro, the carbon emission per linear meter of tunnels built under various surrounding rock conditions is calculated and analyzed. According to the results, the carbon emission per linear meter of tunnel increases markedly in the material production stage and construction stage as the surrounding rock is degraded. In highway tunnel construction, the carbon emission in the material production stage takes the largest proportion, particularly the carbon emission in the secondary lining material production stage takes a high proportion. Therefore improvement of the material production technology and research into carbon emission reduction design of lining structure are the key approaches to reducing total carbon emission in highway tunnel construction.