For the magnet used in power apparatus, the inductance is an important parameter which may change the input-output characteristic of the apparatus. In research of the high temperature superconducting (HTS) magnet in energy storage system and other electric apparatus, we found the difference of the magnet's inductance between normal state and superconducting state. In this paper, the electromagnetic models of Bi2223/Ag tape and windings are established firstly. Based on the simulation analysis and measured results, the reason of inductance variation of HTS magnet has been clarified. The regularity of inductance variation of HTS pancake and magnet has been researched, and new requirement for the veracity in the process of superconducting magnet's design has been claimed.