介绍三门健跳大桥钢管桁架拱采用主塔与扣塔合二为一的无支架吊装方法 ,针对该方法 ,提出相应的施工控制计算方法 .在该桥中 ,笔者首次提出了定长扣索法控制拱助轴线标高的方法 ,给出了节段控制标高和塔架偏位计算公式 .实践证明这种方法是可行的 This paper introduces the method of unsteady hoisting of the steel truss arch of Sanmen jumped bridge with the combination of the main tower and the buckle tower. According to this method, the corresponding construction control calculation method is proposed. In this bridge, The method of controlling the elevation of the arch axis is given and the formula of the height of the section control and the deviation of the tower is given. This method is proved to be feasible