Classical molecular dynamics calculations are performed between 25 and 55 K to investigate the structure and the dynamics of the CO monolayer adsorbed on NaCl(100) surface. The simulation is based on the most recent potential available for this system and the results are compared with experimental data issued from polarization infrared spectroscopy and helium atom scattering. We show that the monolayer adopts a (2x1) structure at 25 K, with two molecules per unit cell. The corresponding angular motions perpendicular and parallel to the surface are clearly librational. As temperature rises, the molecular axes remain tilted with a Librational motion perpendicular to the surface,,while the translational and orientational motions parallel to the surface behave much more freely, leading to an orientationally disordered structure at 55 K. These features suggest that dynamical effects in the (2x1) layer are responsible for an ordered/disordered transition observed as temperature increases, instead of the phase transition from ordered (2x1) to (1x1) structures which was previously inferred.