In this paper, discusses the difference of the rotating speeds between the earth external-shell and internal-core basing on both the internal structure and the theories of gravitation and particle in physics of today. The paper puts the genesis of the generating electricity by the difference of the velocity because the friction mainly causes electricity, and puts the genesis of the dipole magnetic field in the earth. The paper concluds the intensitive formation in any point of rotating axis of internal core in the earth and the method of determining the geomagnetics-pole characteristics, and explains the the critical questions of magnetic axis,magnetic pole drift and polarity transform of geomagnetic field in the geomagnetics.