  MAXI J1820+070 is a newly-discovered black hole X-ray binary, whose dynamical
parameters, namely the black hole mass, the inclination angle and the source
distance, have been estimated recently. \emph{Insight}-HXMT have observed its
entire outburst from March 14th, 2018. In this work, we attempted to estimate
the spin parameter~$a_*$, using the continuum-fitting method and applying a
fully-relativistic thin disk model to the soft-state spectra obtained by
\emph{Insight}-HXMT. It is well know that $a_*$ is strongly dependent on three
dynamical parameters in this method, and we have examined two sets of
parameters. Adopting our preferred parameters: $M$ =
$8.48^{+0.79}_{-0.72}~M_\odot$, $i=63^\circ\pm3^\circ$ and $D=2.96\pm0.33$ kpc,
we found a slowly-spinning black hole of $a_*=0.14 \pm 0.09$ ($1\sigma$), which
give a prograde spin parameter as majority of other systems show. While it is
also possible for the black hole to have a retrograde spin (less than 0) if
different dynamical parameters are taken.
