Cable-stayed bridge, being composed of cable-beam-tower, is a statically indeterminate spatial structure. The reasonable change of cable force and alignment is the safe indemnification of the bridge structure ,However, an obvious change should be surveyed to find out the causes. As a large difference exists in two monitoring of the cable force and alignment of the PC cable-stayed bridge in southwest China, an investigation is taken. In the survey, a three-dimensional simulation model of the bridge is built with the finite element theory, which is employed to study the 4 temperature effects including the range of whole temperature, cable-beam temperature, girder and tower sun-shine temperature difference to eliminate the difference of monitoring time. The results show that different tempera-ture effects have different impacts on one parameter, and one kind temperature effect may have different impacts on different parameters. As cable-beam temperature and girder sunshine temperature difference are the main difference causes of measured able force and alignment in a bridge, it is necessary to take temperature effects into account when assessing the security of PC cable-stayed bridge, to correct the measured data, and to eliminate the temperature effect for reducing cable force and alignment differences significantly, which lays the structure in a safe state.%斜拉桥是由索-梁-塔组成的超静定空间结构，其索力与线形的合理变化是桥梁结构安全运营的保障，对于明显的差异性则须研究其成因。通过对西南地区某既有大跨径PC斜拉桥的索力与线形的监测对比发现存在较大差异性，而外观调查未发现明显的结构性病害。为研究探讨其形成原因，首先运用有限元理论知识建立了桥梁的三维空间仿真分析模型，然后考虑到监测时间的温度差异，针对性地进行了整体升温、索梁正温差、主梁及主塔日照正温差等4种温度效应的研究。研究结果表明：不同的温度效应对某一参数影响不同，同一种温度效应对不同的参数影响不同。就本桥而言，索梁正温差与主梁日照正温差是造成实测索力与线形差异性的主要原因，对既有大跨径PC斜拉桥的安全性评估必须考虑温度效应的影响，需对实测关键参数进行修正，消除温度效应影响后的斜拉桥索力与线形差异性明显减小，结构处于安全状态。
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