Abstract: Based on the strict and delicate analogue relation between the magnetic moment of a rotating charged bodies and moment of inertia of rigid bodies, a new concept of charge moment tensor Ⅰ which is different from the existent electric multipole moment is introduced. And by means of eigenvalue equation of tensor Ⅰ, the concept of principal axes and principal-axis scalar charge moment are constructed, and further the scalar charge moment of a charged body and the magnetic moment of a rotating charged body around an arbitrary direction are attained.

Key words: magnetic moment, moment of inertia, charge moment tensor, scalar charge moment, charge moment ellipsoid, principal axis