Fe(CN)6 vacancies will usually form in the process of Prussian Blue synthetization due to rapid precipitation then will be occupied by water (H2O) molecules. Through first principles calculation, this situation is simulated and the effect of water H2O molecules toward the electronic and structural properties are reported and discussed. In these theoretical calculations, the structural properties and electronic properties of pure PB and hydrated PB have been analysed by using density functional theory (DFT). Based on density functional theory (DFT), generalized gradient approximation (GGAPBE) and GGA+U were used as exchange correlation functionals. As the result, bandgap for GGAPBE+U was obtained 1.66 eV for pure Prussian Blue (PB). The defect and water molecules were found to influence on the bandgap and density of state of this material and 1.033 eV bandgap were obtained. Base on the lattice parameter, the structure of hydrated PB are shrinking and distorted from the ideal cubic. The structure is weakened as the bond order (BO) for the Fe-N drop about half of the original value.