  We studied the kinematics of the Galactic bubble RCW 120 in the
[SII]\lambda\lambda$6717,6731\AA lines. We measured a LSR radial velocity
ranging from ~-74 to ~-6km/s. We found evidence of expansion only in the
northeast region of the nebula (from 20 to 30 km/s). We found a high electron
density around 4000 cm^{-3} in the south-west region and we also found two
arches-like structure indicating a density gradient. We present 3D numerical
simulations of RCW 120 using Walicxe-3D code in order to explore optical shell
dynamics and its morphology. Our numerical results predict an average numerical
electron density of the ambient medium (in the southern region of the object)
is between 3000 to 5000 cm^{-3} in agreement with our values obtained from the
observations. From our models, we do not expect X-ray emission coming from the
external shell, due to the low expansion velocity value.}
