With the increasing reliability of power supply requirements, timely detection of cable defects become the key. The traditional method currently used is to conduct DC voltage withstand test on the cable. This method can only find larger defects, which are difficult to find when the smaller defects are tested. Moreover, the DC voltage withstand test is very harmful to the cable itself and belongs to the high strength Destructive test. The PD oscillation test is through the system detection loop of the cable discharge current in the pulse signal analysis and calculation to achieve the internal cable partial discharge value detection and location determination. Through the use of this new technology, can accurately grasp the operation of cable lines, early detection of potential safety problems, to avoid failure and reduce the accident rate.