The invention relates to an ultra-wideband weak magnetic sensor, which is formed by penetrating a magnetic core formed by adhering a time difference type magnetic-field measurement sensitive component on a high-magnetoconductivity magnetic rod with a square cross section through the center of a skeleton, winding a plurality of induction coils on a groove outside the skeleton and covering the induction coils with a shielding copper sheet. The completion of the high-precision detection from a ground surface to an upper mantle by replacing the sensor necessarily is avoided; as 0.01 Hz is used as a boundary frequency, the precision of an inductive sensor is higher when a frequency is higher than 0.01 Hz; and the precision of a fluxgate type sensor is higher when the frequency is lower than 0.01 Hz. The problem of the low precision of part of frequency ranges caused when a single sensor is used is solved. As changing a low-frequency measuring part into the time difference type fluxgate sensor is adopted, the ultra-wideband magnetic-field measurement of DC-10 kHz can be realized, and the application frequency range of a current earth electromagnetic detection magnetic field sensor is broadened. The too many coils and the too long magnetic core are not necessary to use, and the miniaturization of the sensor is convenient.