The invention provides a ruthenium water oxidation catalyst and a preparation method and application of the catalyst. The ruthenium water oxidation catalyst has a structure described as a general formula I. According to a flexible chain in an axial ligand of the ruthenium water oxidation catalyst, the degree of spatial freedom is increased, and the distance between the ruthenium water oxidation catalyst and a light-sensitive agent can be freely adjusted, so that the electron transfer from the catalyst to the light-sensitive agent is regulated. Moreover, according to the ruthenium water oxidation catalyst, a phosphate adsorption group is introduced into the axial ligand, so that the adsorption property of the catalyst is improved, and the catalyst is difficult to desorb.