In the local discharge detection of cables, the high frequency discharge current is mainly monitored by installing HFCT and other methods in the cable grounding loop, this often leads to problems such as weak coupling of the local discharge signal, 50 Hz circulating current on the grounding wire and high frequency harmonics superimposed with local discharge signal, resulting in a low signal-to-noise ratio, and on-site electromagnetic interference will also be conducted to the sensor through the grounding wire, and the discharge detection effect is not ideal. Considering that the zero-sequence CT installed on the cable core line is similar to the structure of HFCT, this paper explores the method of using-sequence CT to couple the high frequency signal of cable local discharge. Starting from the equivalent circuit, the working principle of zero-sequence CT is theoretically analyzed. Subsequently, the impedance of the zero-sequence CT and the sensitivity of coupling high frequency signals by connecting CT in series at the zero-sequence CT lead-out line and grounding wire are tested and the results show that the zero-sequence CT has the ability to couple high frequency signals and can meet the requirements of local discharge detection.