  We have calculated part of O(${\alpha}_{S}$) QCD radiative correction to the
total cross-section of top's threshold production in $ e^{+}e^{-} \to t\bar t
\to W^{-} b W^{+} \bar b$ reaction. We found out a curious fact: there is no
O(${\alpha}_{S}$) correction to the total cross-section, originated from $b
\bar b , t \bar b ,\bar t b $ gluon exchange and corresponding gluon emission.
Thus, all O(${\alpha}_{S}$) corrections which are non-zero, can be classified
as: 1) corrections to $t \bar t$ nonrelativistic potential 2) corrections to
the top's width 3) hard gluon correction to $\gamma t \bar t$-vertex. These
corrections are well-known and were described in the previous papers. We can
conclude that similar situation takes place for all unstable particles
threshold production. This result can be expressed in the form of a general
statment: There is no O(${\alpha}_{QED}$ or ${\alpha}_{QCD}$) corrections for
the total cross-section , originated from the "jet-jet" interection.
