Abstract: The power cables in modern cities are mainly laid underground,and sometimes the cables will fail due to aging,overload or accidental injury in construction,which will have a huge impact on social life and industrial production.In this paper,we design the power cable fault accurate point detection system,precise fixed-point process often need to use high voltage breakdown fault of power cable,signal generator according to the impact of the sounds made by discharge and pulse magnetic field signal characteristics,by using magnetic synchronous acoustic method to detect the fault point location,but often by detection in the environment impact discharge acoustic noise,so the spectral subtraction in a first for background noise,then waited for prevent misjudgment by short-time energy method,and then accurate judgment,through software simulation test and field data testing,the algorithm precision test method.