Starting from concept of magnetic charge，using analogy with electricity and knowledge of static electricity，we write out directly the expressions for magnetic field and magnetic potential produced by a magnetic pole. Then，the concept of magnetic shell is introduced and its important character is discussed. With the aid of the equivalence of a circuit and a magnetic shell，we can seamlessly convert the knowledge obtained from magnetic charge to almost all the theoretical formula for current，which are taught in every textbooks of steady current magnetism. This approach of teaching may help students to understand magnetic phenomena in a simple but insightful way.