  We present the dynamics study toward the G326.611+0.811 (G326)
hub-filament-system (HFS) cloud using the new APEX observations of both
$^{13}$CO and C$^{18}$O (J = 2-1). The G326 HFS cloud constitutes a central hub
and at least four hub-composing filaments that are divided into a major branch
of filaments (F1, and F2) and a side branch (F3-F5). The cloud holds ongoing
high-mass star formation as characterised by three massive dense clumps (i.e.,
370-1100 $M_{\odot}$ and 0.14-0.16 g cm$^{-2}$ for C1-C3) with the high
clump-averaged mass infalling rates ($>10^{-3}$ $M_{\odot}$ yr$^{-1}$) within
in the major filament branch, and the associated point sources bright at 70
$\mu$m typical of young protostars. Along the five filaments, the velocity
gradients are found in both $^{13}$CO and C$^{18}$O (J = 2-1) emission,
suggesting that the filament-aligned gravitational collapse toward the central
hub (i.e., C2) is being at work for high-mass star formation therein. Moreover,
a periodic velocity oscillation along the major filament branch is revealed in
both $^{13}$CO and C$^{18}$O (J = 2-1) emission with a characteristic
wavelength of $\sim$3.5 pc and an amplitude of $\sim$0.31-0.38 km s$^{-1}$. We
suggest that this pattern of velocity oscillation in G326 could arise from the
clump-forming gas motions induced by gravitational instability. Taking into
account the prevalent velocity gradients, the fragmentation of the major branch
of filaments, and the ongoing collapse of the three massive dense clumps, it is
indicative that G326 is a HFS undergoing global collapse.
