  The proton spin crisis still remains an unsolved problem in particle physics.
It is suggested in the literature that the gauge invariant spin and orbital
angular momentum of the quark and the gauge invariant total angular momentum of
the gluon contribute to the proton spin. However, in this paper we find a new
contribution to the proton spin. This new contribution is due to the boundary
surface term in the total angular momentum conservation equation in QCD which
is non-zero due to the confinement of the quarks and gluons inside the finite
size proton. We derive the non-perturbative formula of this new contribution to
the proton spin which can be calculated by using the lattice QCD method.
