This work reports the real-time observation of the interlayer lattice vibrations in bilayer and few-layer ${\mathrm{PtSe}}_2$ by means of the coherent phonon method. The layer-breathing mode and standing wave mode of the interlayer vibrations are found to coexist in such a kind of group-10 transition metal dichalcogenides (TMDCs). The interlayer breathing force constant standing for perpendicular coupling (per effective atom) is derived as 7.5 N/m, 2.5 times larger than that of graphene. The interlayer shearing force constant is comparable to the interlayer breathing force constant, which indicates that ${\mathrm{PtSe}}_2$ has nearly isotropic interlayer coupling. The low-frequency Raman spectroscopy elucidates the polarization behavior of the layer-breathing mode that is assigned to have ${\mathrm{A}}_{1\mathrm{g}}$ symmetry. The standing wave mode shows redshift with the increasing number of layers, which successfully determines the out-of-plane sound velocity of ${\mathrm{PtSe}}_2$ experimentally. Our results manifest that the coherent phonon method is a good tool to uncover the interlayer lattice vibrations, beyond the conventional Raman spectroscopy limit. The strong interlayer interaction in group-10 TMDCs reveals their promising potential in high-frequency ($～\text{terahertz}$) micro-mechanical resonators.