  Combing Gaia DR2 with LAMOST DR5, we spectroscopically identified 924 hot
subdwarf stars, among which 32 stars exhibit strong double-lined composite
spectra. We measured the effective temperature $T_{\rm eff}$, surface gravity
$\log\,g$, helium abundance $y=n{\rm He}/n{\rm H}$, and radial velocities of
892 non-composite spectra hot subdwarf stars by fitting LAMOST observations
with Tlusty/Synspec non-LTE synthetic spectra. We outlined four different
groups in the $T_{\rm eff}-\log\,g$ diagram with our helium abundance
classification scheme and two nearly parallel sequences in the $T_{\rm
eff}-\log(y)$ diagram. 3D Galactic space motions and orbits of 747 hot subdwarf
stars with $(G_{BP}-G_{RP})_{0}<-0.36$ mag were computed using LAMOST radial
velocities and Gaia parallaxes and proper motions. Based on the $U-V$ velocity
diagram, $J_{z}-$eccentricity diagram, and Galactic orbits, we derived Galactic
population classifications and the fractional distributions of the four hot
subdwarf helium groups in the halo, thin disk and thick disk. Comparisons with
the predictions of binary population synthesis calculations (Han 2008) suggest
that He-rich hot subdwarf stars with $\log(y)\ge0$ are from the double helium
white dwarfs merger, He-deficient hot subdwarf stars with $-2.2\le\log(y)<-1$
from the common envelope ejection, and He-deficient hot subdwarf stars with
$\log(y)<-2.2$ from the stable Roche lobe overflow channels. The relative
number of He-rich hot subdwarf stars with $-1\le\log(y)<0$ and $\log(y)\ge0$ in
the halo is more than twice the prediction of Zhang et al.(2017), even more
than six times in the thin disk, which implies that the mergers of helium white
dwarfs with low mass main sequence stars may not be the main formation channel
of He-rich hot subdwarf stars with $-1\le\log(y)<0$, specially in younger
environments.
