输电线路弧垂是线路设计和运行维护的主要指标之一，弧垂的大小直接影响到线路的安全稳定运行。分析了架空电力线在两杆塔之间的悬挂状态，当架空线的档距一定时，线路的悬垂状态只要一个独立的变量就可以确定下来。通过分析部分段线路的图像，提取出架空线悬垂状态的独立变量，从“悬链段”恢复出完整的水平悬链线，进而计算出档距一定的架空线路的弧垂。对两端等高线路及两端不等高线路进行了仿真实验，实验表明，该方法能较好的恢复出完整线路曲线，计算出线路弧垂。

Sag of transmission line is one of the main indexes for circuit design, running and maintenance. It directly impacts on the safety of the operation. Analyzing the hanging state of overhead power line between the two towers, the overhanging state of line can be determined by an independent variable when the span length is certain. By analyzing the sectional power line image, the independent variable can be extracted and the aclinic catenary can be restored based on the catenary-segment. Then the sag would be calculated. Both two end contour line and non-contour line are simulated by the method. And the experiment had indicated that it is efficacious.