  We study the impact of the full ${\cal O}(\alpha_{s})$ QCD and ${\cal
O}(\alpha_{ew})$ electroweak (EW) radiative corrections to the $e^+e^- \to t
\bar t Z^0$ process in the standard model (SM), and investigate the dependence
of the lowest-order(LO), one-loop QCD and EW corrected cross sections on
colliding energy $\sqrt{s}$. The LO, QCD and EW corrected spectrums of the
invariant mass of $t\bar t$-pair and the distributions of the transverse
momenta of final top-quark and $Z^0$-boson are presented. The numerical results
show that the one-loop QCD correction enhances the LO cross section, but the EW
one-loop correction generally suppresses the LO cross section with our chosen
parameters. In the case of $m_H=120 GeV$, the QCD relative corrections can
reach 43.16% when $\sqrt{s} = 500 GeV$, while the EW relative corrections have
the values of -9.24%, -4.36% and -5.81%, when $\sqrt{s} = 500 GeV$, $800 GeV$,
1.2 TeV$, respectively.
