A new Keggin-type polyoxometalate-based supramolecular complex 1, namely H3［(3-PA)4(PW12O40)］ (3-PA=3-Pyridineacrylic acid), was successfully synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction, elemental analysis (EA), IR spectra, PXRD, TG and UV-Vis diffuse-reflectance. Complex 1 crystallizes in the triclinic system, P-1 space group with a=1.200 33(3) nm， b=1.216 42(3) nm, c=1.424 66(4) nm, α=75.030(1)°, β=73.452(1)°, γ=69.372(1)°, V=1.837 00(8) nm3, Z=1, Mr=3 476.78, F(000)=1 538, μ=18.815 mm-1, Dc=3.143 mg·m-3, S=1.062, R1=0.046 2, wR2=0.138 7. The structural unit of complex 1 consists of a ［PW12O40］3- ployanion and four 3-PA ligands. In addition, ［PW12O40］3- polyanion and 3-PA ligands are linked by H-bonds to form 2-D supramolecular layer. When using as photocatalyst, complex 1 displayed excellent photocatalytic activity towards the reduction of Cr(Ⅵ) with good structural stability and recyclability.