A molecular dynamics approach has been employed to study the dynamical behavior of a water droplet adsorbed on a poly(methyl methacrylate) (PM MA) surface. Several sizes of water droplets are considered in order to understand the size influence of the droplet oil the dynamical properties of water molecules oil the PM M A substrate. The local density profile of water molecules ill the droplet upon impact with the PMMA surface is calculated, and the result shows,S an increase in water penetration with a decrease in the size of the droplet. By examining the velocity field, the regular motion of the water droplet is Found both during the equilibrium process and after the droplet reaches the equilibrium state. The dynamical behavior of water Molecule is Studied by the velocity autocorrelation function (VACF) in different regions for different sizes of water droplets. The result shows that VACFs in different regions are significantly influenced for the droplet with 500 water molecules than for that with 2000 water molecules. Calculations in different regions are made for the vibrational spectrum of the oxygen atom, as well as for hydrogen bond dynamics, the lifetime, and the relaxation time of the hydrogen bond. The changes in the hydrogen bond dynamics are consistent with the change in the distribution of the hydrogen bond angle. We conclude that the dynamical properties of the water molecule are significantly affected by the region relative to the surface but only weakly influenced by the size of the droplet.