  Pseudospin symmetry (PSS) is a relativistic dynamical symmetry connected with
the lower component of the Dirac spinor. Here, we investigate the conservation
and breaking of PSS in the single-nucleon resonant states, as an example, using
Green's function method that provides a novel way to precisely describe not
only the resonant energies and widths but also the spacial density
distributions for both narrow and wide resonances. The PSS restoration and
breaking are perfectly displayed in the evolution of resonant parameters and
density distributions with the potential depth: In the PSS limit, i.e., when
the attractive scalar and repulsive vector potentials have the same magnitude
but opposite sign, PSS is exactly conserved with strictly the same energy and
width between the PS partners as well as identical density distributions of the
lower components. As the potential depth increases, the PSS is broken gradually
with energy and width splittings and a phase shift in the density
distributions.
