The equilibrium structure, harmonic frequency and dissociation energy of the ground state of OH are calculated using density functional theory (B3LYP) method and quadratic CI method including single, double and triple substitutions (QCISD(T)). Based on the theory of atomic and molecular statics, the reasonable dissociation limit for the ground state (X2Π) of OH is derived. The potential energy curve and relevant optical constants of this state are obtained by least square fitting to the Murrell-Sorbie function. All calculation results are in good agreement with the experimental data.