  We measure the cross-correlation between galaxy groups constructed from DESI
Legacy Imaging Survey DR8 and \emph{Planck} CMB lensing, over overlapping sky
area of 16876 $\rm deg^2$. The detections are significant and consistent with
the expected signal of the large-scale structure of the universe, over group
samples of various redshift, mass, richness $N_{\rm g}$ and over various scale
cuts. The overall S/N is 40 for a conservative sample with $N_{\rm g}\geq 5$,
and increases to $50$ for the sample with $N_{\rm g}\geq 2$. Adopting the
\emph{Planck} 2018 cosmology, we constrain the density bias of groups with
$N_{\rm g}\geq 5$ as $b_{\rm g}=1.31\pm 0.10$, $2.22\pm 0.10$, $3.52\pm 0.20$
at $0.1<z\leq 0.33$, $0.33<z\leq 0.67$, $0.67<z\leq1$ respectively. The group
catalog provides the estimation of group halo mass and therefore allows us to
detect the dependence of bias on group mass with high significance. It also
allows us to compare the measured bias with the theoretically predicted one
using the estimated group mass. We find excellent agreement for the two high
redshift bins. However, it is lower than the theory by $\sim 3\sigma$ for the
lowest redshift bin. Another interesting finding is the significant impact of
the thermal Sunyaev Zel'dovich (tSZ). It contaminates the galaxy group-CMB
lensing cross-correlation at $\sim 30\%$ level, and must be deprojected first
in CMB lensing reconstruction.
