Fault-path-coupling positioning method and multi-path-apparatus detecting method

First, if tested result of cascaded channels in a faulty section is abnormal, and tested results of all subdivided sub intervals are all normal, the method can determine that coupling faults are existed between some sub intervals. Next, one sub interval is as a positioning interval, and the other sub intervals are as assist interval. Then the positioning interval is divided into two sub intervals; test of cascaded channels is carried out for the said one sub interval and the assist interval respectively; the sub interval with abnormal tested result is as the positioning interval, which is divided into two smaller sub intervals, and test of cascaded channels is carried out for one smaller sub interval and assist interval respectively till channel with abnormal result in test of cascaded channels for all sub intervals and assist interval is found finally. According to the method, fault channel in other sub intervals can be positioned.