  The conflict between cononical commutation relation and gauge invariance,
which both the momentum and angular momentum of quark and gluon should satisfy,
is clarified. The quantum version of gauge invariance is studied. The gauge
independence of the matrix elements of quark momentum and angular momentum
operators between physical states are proved. We suggest to use the canonical
quark momentum and angular momentum distributions to describe the nucleon
internal structure in order to establish an internal consistent description of
hadron spectroscopy and hadron structure. The same problem for the atomic
spectroscopy and structure is discussed.
