A nickel complex with a three-dimensional supramolecular structure was synthesized through mixed solvent refluxing method using 3-(4-carboxyphenyl)-7-methyl-2-propyl-3H-benzo［d］imidazole-5-carboxylic acid and NiCl2·6H2O as raw material. Its structure and property were characterized by X-ray single crystal diffraction, elemental analysis, IR, UV-Vis and fluorescence spectra. Single crystal X-ray diffraction studies reveal that the complex is in the triclinic system, space group of P1 with a=0.778 5(16) nm, b=1.126 6(2) nm, c=1.175 6(2) nm, α=113.63(3)°, β=93.24(3)°, γ=101.00(3)°, V=0.917 1(3) nm3. The title complex is a mononuclear complex which consists of four ligand anions that connect the center Ni(II) cation to form a one-dimensional ring chain, and further forms a three-dimensional supramolecular structure through hydrogen bonding and π-π stacking. Fluorescence spectrum analysis shows that both the ligand and the title complex have good fluorescence properties, and the fluorescence properties of the title complex are better than that of the ligand.