  The spin current $J_{S}$, orbit angular momentum current $J_{L}$ and total
angular momentum current $J_{J}$ in a dyad form have been universally defined
according to quantum electrodynamics. Their conservation quantities and the
continuity equations have been discussed in different cases. Non-relativistic
approximation forms are deduced in order to explain their physical meanings,
and to analyze some experiment results. The spin current of helical edge states
in HgTe/CdTe quantum wells is calculated to demonstrate the properties of spin
current on the two dimensional quantum spin-Hall system. A generalized
spin-orbit coupling term in the semiconductoring media is deduced based on the
theory of the electrodynamics in the moving media. We recommend to use the
effective total angular momentum current instead of the pure spin current to
describe the polarizing distribution and transport phenomena in spintronic
media.
