It is difficult to identify and locate the defects quickly when the long cable line cross-bonded box has defects such as grounding,water inflow and three-phase sequence error. Aiming at three types of typical defects of cross-bonded box,a cross-bonded model of long cable lines is established to analyze the amplitude and phase change rule of circulation under the defects. Then,the curve fitting of the ratio of circulation at both ends and the scatter data of defect box number are carried out to obtain the defect location formulas. Finally,it is verified by an example. The results show that the circulation amplitude of the defective phase increases and the non-defective phase is normal when the ground is grounded inside the box. When the phase sequence is wrong,the amplitude of two-phase circulation increases obviously,and the amplitude of the other phase circulation is smaller. When the tank is filled with water,the circulation amplitude of each phase increases and is basically equal. The fitting degree of the positioning formula is about 0.96,and the range of defect box number can be determined through the example verification. The proposed method is not affected by the change of wire core current and ground resistance,and can provide reference for the defect identification and location of long cable line cross-bonded box.