The main bridge of San′an Yijiang River Bridge on Nanning‐Qinzhou Railway is a three‐span continuous steel truss arch bridge with span arrangement of (132+276+132) m .The steel girder of the main bridge was erected from the two side spans towards the central span and closed at the midspan of the central span .To ensure that the bridge in completed bridge state could meet the targeted geometrical shape and internal force condition ,the erection process was moni‐tored and controlled .Based on the theory of unstressed state control method ,the finite element program was used to establish the spatial calculation model of the steel truss arch bridge and for‐mulate the monitoring scheme .In the process of cantilever assembly of the steel girder ,the de‐formation of the steel truss arch bridge ,load bearing condition and the mechanical behavior of ma‐jor auxiliary construction facilities (temporary hanger cables) were monitored .During the process in which the steel girder was assembled in cantilever way to the closure stage at the midspan ,the deformation and displacement of the structure was monitored to determine the moving and lowering amount of the beams .When the moving and lowering adjustment of the beams was completed ,the displacing state of the structure was monitored .According to the width and temperature variation of the closure gap ,at the highest temperature time during a day ,the steel girders on the two sides were pushed to adjust the width of the lower chord closure gap to realize the closure of the lower chord of the steel girder .After the closure of the arch ribs ,the side piers on the two banks were jacked up to make the dimension of the closure gap of the deck reach design width to realize the un‐stressed closure of the deck .After the closure of the deck ,according to the calculation results from the monitoring and control ,the hanger cables on the Nanning side were first dismantled ,and then the ones on the Qinzhou side .The monitoring results in the completed bridge state demon‐strate that the actual precambers of all the panel points of the main truss agree well with the theo‐retical values ,with an error limited within 2 mm ,and the geometry of the structure is smooth .%南钦铁路三岸邕江特大桥主桥为（132＋276＋132） m三跨连续钢桁拱桥，主桥钢梁从两侧边跨向中跨架设、在中跨跨中合龙。为了使桥梁在成桥状态达到目标几何线形和内力状态，对架设过程进行监控。在无应力控制法理论基础上，利用有限元程序建立钢桁拱桥空间计算模型，制定监控方案。钢梁拼装架设过程中，对钢桁拱桥变形、受力及主要辅助施工设施（临时吊索）受力进行监控。在钢梁悬拼至跨中合龙阶段，监测结构变形变位情况，确定相应的移落梁调整数值。预先移落梁调整后，监测结构变位情况，按照合龙口宽度和温度变化的规律，在一天最高温度时，通过对拉两岸钢梁调整下弦合龙口宽度，实现钢梁下弦合龙。拱肋部分合龙完毕，起顶两岸边墩使系杆合龙口尺寸达到设计宽度，实现系杆无应力合龙。系杆合龙后，根据监控计算结果，先拆南宁岸吊索，后拆钦州岸吊索。成桥阶段监控结果显示：主桁各节点实际预拱度与理论预拱度符合较好，误差在2 mm以内，结构线形平顺匀滑。
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