  The soft pion correction at high energy may play a crucial role in
non-perturbative parts of sea quark distributions. In this paper, we show that,
while the soft pion correction for the strange sea qaurk distribution is
suppressed in the large and the medium $x$ region compared with that for the up
and the down sea quark one, it can become large and SU(3) flavor symmetric in
the very small $x$ region. This gives us a good reason for the symmetry
restoration of light sea quark distributions required by the mean charge sum
rule for the light sea quarks. Then, by estimating this sum rule with the help
of the results obtained by the soft pion correction, it is argued that there is
a large symmetry restoration of the strange sea quark in the region from
$x=10^{-2}$ to $10^{-6}$ at $Q^2\sim 1$ GeV.
