A Keggin-type polyoxometalate-based supramolecular complex H3［{H(4-AP)}6(PMoV6MoVI6O40)］ (4-AP=4-aminopyridine) was successfully synthesized from ammonium molybdate, nickel chloride, and 4-aminopyridine by hydrothermal method. The structural unit of the complex contains a ［PMoV6MoVI6O40］9- anion and six protonated ligands. ［PMoV6MoVI6O40］9- anion and ligands are connected to each other by N(1)-H(1)…O(3), N(2)-H(2A)…O(5), and N(2)-H(2B)…O(1) hydrogen bonds, which further form a two-dimensional supramolecular layer. It was characterized by X-ray single crystal diffraction, IR spectra, and powder X-ray diffraction. The crystal structure analysis shows that the complex belongs to the trigonal crystal system, R-3 space group, a=2.191 2 (10) nm, b=2.191 2 (10) nm, c=1.042 3 (5) nm, α=β=90°, γ=120°, V=4.333 8 (4) nm3, Z=3, R1=0.036 2, wR2=0.095 6. The electrocatalytic performance shows that the complex has a good electrocatalytic reduction effect on H2O2 and K2Cr2O7. It also has a good effect of electrocatalytic oxidation on ascorbic acid.