The invention discloses a rare earth metal organic framework material, which has a chemical formula: {[(CH3)2NH2][Eu4(FDA)7(DMF)2.0.5DMF]}n. A preparation method of the framework material comprises the following steps: (1) respectively dissolving organic ligands H2FDA and 4,4'-diphenyldicarboxylic acid in N,N-dimethylformamide solvent; (2) dissolving Eu(NO3)3.6H2O in a N,N-dimethylformamide solvent containing nitric acid; (3) mixing the above two solutions, placing the mixture into a sealed hydrothermal reaction kettle, carrying out a reaction at a constant temperature for 72 hours, separatingsolids from products which are taken out from the reaction kettle; and (4) washing the solids for a plurality of times with N,N-dimethylformamide to obtain a colorless block-shaped crystal. The abstract drawings are three-dimensional structural drawings of the framework material. The preparation method of the framework material is simple and convenient in synthesis, easy to implement, high in yield, low in cost, good in reproducibility, stable in water and stable in solvents. The framework material can be used to detect the presence of Cr(VI) ions in water by fluorescence quenching effects.