Abstract: The viaduct project of the second ring road in Chengdu is located in the heart of the old town，in order to ensure the normal traffic of vehicles during the construction of the capping-beam-support-system with high buttress ( the average height of 12 m) and long cantilever ( the average length of 10. 3 m) ，a set of complete support system for capping beam construction was designed，including comparison of three kinds of mechanical system schemes; the mechanical analysis and designs of foundation，security system and installation process of the optimized scheme． Construction results showed the optimized scheme satisfied the requirements of design lines and faced concrete． A set of application methods was provided for similar entities pier capping beam construction．