  We investigate the vertical structure and elements distribution of
neutrino-dominated accretion flows around black holes in spherical coordinates
with the reasonable nuclear statistical equilibrium. According our
calculations, heavy nuclei tend to be produced in a thin region near the disk
surface, whose mass fractions are primarily determined by the accretion rate
and the vertical distribution of temperature and density. In this thin region,
we find that $^{56}\rm Ni$ is dominant for the flow with low accretion rate
(e.g., $0.05 $$M_{\odot}$ $\rm s^{-1}$) but $^{56}\rm Fe$ is dominant for the
high counterpart (e.g., $1 M_{\odot}$ $\rm s^{-1}$). The dominant $^{56}\rm Ni$
in the special region may provide a clue to understand the bumps in the optical
light curve of core-collapse supernovae.
