The electrical method is effective on detecting and locating leaks in geomembrane liners for landfills. If a leak exists in the liner, an anomaly in the measured potential is generated in the immediate vicinity of the leak through which electrical current is flowing. But the power supply current above the liner can affect the potential distribution. A current point source model for power supply current was set up in this paper. The potential equation induced by the point source was derived. The analysis of potential expression shows that: 1) the potential generated by the power supply current is proportional to the current size and the medium resistivity; 2) as the medium thickness increases, the potential reduces; 3) to reduce the influence of power supply current, the power supply electrode should be away from the detection area as far as possible.