In the reconstruction of urban power distribution networks, the exact location of many old directly buried cables is unknown, which has brought certain difficulties to the work of patrolling and locating faulty cables. In this paper, a method for detecting underground cables based on the analysis of magnetic field component waveforms is studied. This method is also applicable to the detection of submarine cables. The method uses a fluxgate sensor to detect the weak cable magnetic field. Three mutually perpendicular components of the magnetic field are measured separately. To simulate a real live cable, an experiment system to simulate the operation of the cable is established. Results show that at least two of the three magnetic field components have specific peaks and valleys, and these peaks and valleys are related to the location of the cable. Using the distribution characteristics of the two component waveforms can accurately locate the cable. It is found that for AC cables, the measurement results are effectively readable when the magnetic field frequency is an integer multiple of the sampling frequency. In addition, this study also uses simulation software to analyze the significant weakening effect of the cable shielding layer on the magnetic field generated by the cable.