An extensive search for stable chemisorbed SO2 Configurations on the Pt(111) surface has been performed using first-principles DFT-GGA calculations. The most energetically stable configurations, eta(2)-S-b,O-a and eta(3)-S-a,O-a,O-a at fcc sites, where eta(2) and eta(3) mean that the number of atoms of the adsorbate coordinated to surface atoms are two and three, respectively, and the subscripts a and b stand for the atoms on atop sites and bridge sites, respectively, are consistent with experimental observations. It is found that strong sulfur-metal bonds are essential in stabilizing the molecular SO2 binding to the Pt(111) surface. The lateral dipole-dipole interactions among chemisorbed SO2 moieties are shown to be responsible for the strong coverage effect of the SO2 binding energy to the surface. These strong lateral interactions do not greatly affect the molecular structures or relative binding energy differences among different binding configurations. The projected density of states and the induced density of states are studied in detail to explain binding effects.