采用化学成分分析、金相检验、显微硬度测试及断口宏观和微观形貌观察等方法对前后两天断裂的两根海上拖缆的断裂原因进行了分析。结果表明: 断裂的两根拖缆都是由于拖力波动较大,使得拖缆内股钢丝绳瞬间负载过大,超过其抗拉强度首先发生断裂，继而导致外股钢丝绳发生过载断裂,从而瞬间形成整绳断裂。

Two marine towlines fractured one after another in two days. The fracture reason was analyzed by means of chemical compositions analysis, metallographic examination, micro-hardness test and fracture analysis. The results show that the two times of fracture both occurred under cycle and over-loading. The fracture process was that the core lines of the towline fractured firstly and then the external lines fractured, so the whole towlines fractured in a short time.