根据黑岩子“耐—直—耐”长江大跨越的特点，分别观测了档内子导线弛度，进行了地面划印割线计算，以控制观测档子导线弛度。挂线后弛度复测结果表明：该弛度观测方式及割线计算方法能够确保导线弛度误差及子导线误差符合规范要求。

According to the features of large crossing of stain-tangent-strain style at Heiyanzi of the Yangzi River,the catenary control method is applied,by which sub-conductor sags are observed and the removed-length is calculated by ground marking.It is shown from the repetition measurement of assembled-conductor sags that the sag measurement and the secant calculation method are efficient for the conductor sag and sub-conductor errors meeting the demands of design requirements.