Abstract: The research into magnetic dipole theory can be applied to: ① deepen the cognition for magnetic leakage field yielded by discontinuities; ② understand the physical basis of magnetic NDT. ③ obtain basic law of magnetic NDT. ④ clarify experimental phenomena, which are contrary to the traditional principle of magnetic NDT. ⑤ solve for analytic expressions of classical experimental results. ⑥ guide the correct design of standard testing specimen. ⑦ provide new conception and new theory for magnetic NDT. ⑧ lay a theoretical foundation for the establishment of equivalent slot standard system in magnetic NDT. All of these are for the sake of real realization of quantification and automation in magnetic NDT technique.