Power cable for power transmission has been gradually extended. The outlet lines in distribution system therefore are more constituted with overhead lines, cables and hybrid lines. The system can be still running 1-2 hours when single phase to earth fault occurs, which requires the location of the fault is detected in the case of UPS. A method of power cable fault location online in neutral point ineffectively grounded power system based on HHT is proposed in this paper. Singularity detection method by which fault line selection can be achieved is used to determine the polar of each line at fault time. Under the condition that the parameters of lines are unknown, the velocity of traveling wave in cable can be measured by the use of switching overvoltage wave which is generated when the closing occurs. The modulus can be obtained by the method of phase-mode transformation when single phase to earth fault happens. HHT, which has a strong completeness and adaptability, is used to process the non-stationary modulus and find the mutations moments of instantaneous frequency. Then the location of line fault is determined by one-terminal fault location method. Finally, the digital simulation results of an example show the effectiveness and practicability of this method.