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The tilt of the velocity ellipsoid is a helpful tracer of the gravitationalpotential of the Milky Way. In this paper, we use nearly 140,000 RC starsselected from the LAMOST and Gaia to make a detailed analysis of the tilt ofthe velocity ellipsoid for various populations, as defined by the stellar agesand 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 samplestars are accurately described as $\alpha$ = $\alpha_{0}$ $\mathrm{arctan}$($Z$/$R$) with $\alpha_{0}$ = (0.68 $\pm$ 0.05). This indicates the alignmentof velocity ellipsoids is between cylindrical and spherical, implying that anydeviation from the spherical alignment of the velocity ellipsoids may be causedby the gravitational potential of the baryonic disk. The results of variouspopulations suggest that the $\alpha_{0}$ displays an age and populationdependence, 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, meaningthat the velocity ellipsoids of the kinematically relaxed stars are mainlydominated 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. Theoscillations in $\alpha_{0}$ appear in both kinematically hot and coldpopulations, indicating that resonances with the Galactic bar are the mostlikely origin for these oscillations.

The tilt of the velocity ellipsoid of different Galactic disk populations