In order to obtain the operating voltage phase of MV cable online and to provide phase information for PD detection, an apparatus and a method for locating the voltage phase of MV cable are provided herein. Using the homemade metal patch sensor to obtain the coupling voltage from the cable termination. The oscilloscope will obtain a partial pressure signal the operating voltage phase will be forecasted by pushing back the voltage phase information which is obtained by oscilloscope. The voltage phase locating device consists of metal patch sensor, oscilloscope and coaxial cable. In this paper, the phase angle between the voltage phase measured by the phase locating device and the phase of the actual operating voltage is calculated by the equivalent and theoretical derivation of the circuit model of the phase locating device. Finally, the test was carried out on the 10kV cable terminal to demonstrate the correctness of the theoretical analysis and the reliability of the method. In the course of the experiment, it also explores the influence on the voltage phase shift angle when testing at different positions of medium voltage three-phase cable terminals. And find the best place to text.