  The tilt of the velocity ellipsoid is a helpful tracer of the gravitational
potential of the Milky Way. In this paper, we use nearly 140,000 RC stars
selected from the LAMOST and Gaia to make a detailed analysis of the tilt of
the velocity ellipsoid for various populations, as defined by the stellar ages
and chemical information, within 4.5 $\leq$ $R$ $\leq$ 15.0 kpc and $|Z|$
$\leq$ 3.0 kpc. The tilt angles of the velocity ellipsoids of the RC sample
stars are accurately described as $\alpha$ = $\alpha_{0}$ $\mathrm{arctan}$
($Z$/$R$) with $\alpha_{0}$ = (0.68 $\pm$ 0.05). This indicates the alignment
of velocity ellipsoids is between cylindrical and spherical, implying that any
deviation from the spherical alignment of the velocity ellipsoids may be caused
by the gravitational potential of the baryonic disk. The results of various
populations suggest that the $\alpha_{0}$ displays an age and population
dependence, with the thin and thick disks respectively values $\alpha_{0}$ =
(0.72 $\pm$ 0.08) and $\alpha_{0}$ = (0.64 $\pm$ 0.07), and the $\alpha_{0}$
displays a decreasing trend with age (and [$\alpha$/Fe]) increases, meaning
that the velocity ellipsoids of the kinematically relaxed stars are mainly
dominated by the gravitational potential of the baryonic disk. We determine the
$\alpha_{0} - R$ for various populations, finding that the $\alpha_{0}$
displays oscillations with $R$ for all the different populations. The
oscillations in $\alpha_{0}$ appear in both kinematically hot and cold
populations, indicating that resonances with the Galactic bar are the most
likely origin for these oscillations.
