Abstract: Hyperfine interaction is one of the important contents in the course of“Atomic Physics”. So far in

domestic and foreign textbooks of atomic physics，authors just write down the expressions of splittings of atomic energy

levels caused by the magnetic hyperfine interaction without and with an external magnetic field，and show some

related research examples. Here，for the cases of without and with a weak or a strong external magnetic field，the

derivation processes of these formulas and discussions about diagram drawing of these splitted energy levels are described

in details. The contents in this paper will be helpful for teachers and students in understanding and truly

mastering the related parts of knowledge in the course of“Atomic Physics”.

Key words: hyperfine interaction, nuclear magnetic dipole moment, splittings of atomic energy levels in an external magnetic field, diagram of atomic energy level, atomic physics