  Hub-filament systems are suggested to be birth cradles of high-mass stars and
clusters, but the formation of hub-filament structure is still unclear. Using
the survey data FUGIN $^{13}$CO (1-0), C$^{18}$O (1-0), and SEDIGISM $^{13}$CO
(2-1), we investigate formation of hub-filament structure in W33 complex. W33
complex consists of two colliding clouds, called W33-blue and W33-red. We
decompose the velocity structures in W33-blue by fitting multiple velocity
components, and find a continuous and monotonic velocity field. Virial
parameters of Dendrogram structures suggest the dominance of gravity in
W33-blue. The strong positive correlation between velocity dispersion and
column density indicates the non-thermal motions in W33-blue may originate from
gravitationally driven collapse. These signatures suggest that the filamentary
structures in W33-blue result from the gravitational collapse of the compressed
layer. However, the large scale velocity gradient in W33-blue may mainly
originate from the cloud-cloud collision and feedback of active star formation,
instead of the filament-rooted longitudinal inflow. From the above observed
results, we argue that the cloud-cloud collision triggers formation of
hub-filament structures in W33 complex. Meanwhile, the appearance of
multiple-scale hub-filament structures in W33-blue is likely an imprint of the
transition from the compressed layer to a hub-filament system.
