The electro-magnetic force controlling pulsing injection of metallogenic fluid is growing a spot of study on metallogenic mechanism. To discuss the principle of electro-magnetic force, the electro-magnetic characters of wall rocks and ores, the relations among flow electric potential, electro-magnetic behaviour of element and driving push stress, the following view points were concluded. ①The electro-magnetic force was a kind of impersonality subsistent force and a kind of surface, similar to tectonic and gravitational forces, all of which could be able to impulse pulsing injection of fluid or metallogenic fluid. ②The electro-magnetic force, different from other powers, was both a surface force and a physical one, which impulsed the fluid movement and affected the particles simultaneously. The attached electro-magnetic force, obtained by changes of geomagnetic pulsing, tectonic energy and heat energy, resulted in the original electro-magnetic force strengthened, the positive and negative ions’ moving quickened and enriched, so as to form ore-bearing fluid easily. Furthermore, the attached force increased the flow electric potential, created an impulsing force to push the metallogenic fluid pulsing injection. ③The invariable electro-magnetic force caused metallogenic elements enriching, mineral assemblages compounding, and vertical or horizontal ore zonations appearing, since the useful elements or minerals having varied electro-magnetic behaviours. ④The electro-magnetic force might be one of primary factors for elements moving, enriching and forming ore-bearing fluid.