| The adsorption characteristics of H2O on CaCO3 (104) surface were studied by the first principle. First, we study 8 high symmetry adsorption structural models of H2O molecules on the top position, bridge position (short bridge position, long bridge position) and hollow position on the CaCO3 (104)surface, respectively, with vertical and parallel surfaces. Combined with adsorption energy and stable adsorption conformation, the optimal adsorption site was determined. Then, based on the H2O / CaCO3 (104) optimal adsorption structure model, we study the variation of the physical structure and the electronic structure (Mulliken population analysis, the density of state, electron localization function) of the H2O / CaCO3 (104) system. Based on that we analyzed the interaction between H2O / CaCO3 (104) surface. Results showed that the most stable adsorption structure is hollow-parallel, based on the stable conformation and the adsorption energy of H2O / CaCO3 (104) system. After the adsorption of H2O on the CaCO3 (104)surface, the O-H bond length and the H-O-H bond angle of H2O molecules are all changed, and the atomic positions of CaCO3 (104) crystals in the direction of parallel and vertical to (104) surface are also changed, in which atoms of the surface layer changes most. That is, the adsorption has great influence on the physical structure of H2O and CaCO3 crystals. Study on the Mulliken population analysis, the density of state and the electron localization function of the H2O / CaCO3 (104) showed that there exist electron transfer between H2O molecule and CaCO3 (104) and bond is formed. Ca-O (H2O) is an ionic bond and H (H2O) -O (CaCO3 ) is hydrogen bonds.