  We compute the fermion spin distribution in the vortical fluid created in
off-central high-energy heavy-ion collisions. We employ the event-by-event
(3+1)D viscous hydrodynamic model. The spin polarization density is
proportional to the local fluid vorticity in quantum kinetic theory. As a
result of strong collectivity, the spatial distribution of the local vorticity
on the freeze-out hyper-surface strongly correlates to the rapidity and
azimuthal angle distribution of fermion spins. We investigate the sensitivity
of the local polarization to the initial fluid velocity in the hydrodynamic
model and compute the global polarization of {\Lambda} hyperons by the AMPT
model. The energy dependence of the global polarization agrees with the STAR
data.
