Research conclusions：The Dashengguan Yangtze Rive Bridge is a tri-steel truss and six-span continuous arch bridge with two main arch spans in the middle and two side spans on the both ends. The general scheme of using double cantilevers to erect the steel truss of the middle main pier, using single cantilever to erect the steel truss of the two side main piers and conducting closure in the middle of the two main arches was adopted for the closure of the main arch of this bridge. Through the analysis of the monitoring computation and the study on the closure measures for the main arch of the steel truss arch bridge with three main trusses, the series of closure measures were taken for accurate closure of the two main arches of the bridge, such as using long circle hole, circle hole, dowel, pushing and pulling device and temperature difference.