A novel organic-inorganic hybrid polyoxometalate（C₅H₇N₂O₂）₄（SiMo₁₂O₄₀）（short for SiMo-12） was synthesized by the conventional aqueous solution method.The compounds were characterized by infrared spectroscopy（IR）,thermogravimetric analysis（TG）,single crystal and powder X-ray diffraction（XRD） and elemental analysis.With hydrogen peroxide as oxidant,SiMo-12 was used to catalyze the oxidation of iodine ions.The effect of catalyst dosage,oxidant dosage,pH,temperature and other factors on the reaction rate were investigated.The results showed that the compound belonged to the triclinic crystal system,P-1 spatial group,cell parameters a=1.097 58（4） nm、b=1.144 88（4） nm、c=1.252 66（4） nm、α=64.665（1）°、β=64.804（1）°、γ=83.441（1）°、V=1.282 89（8） nm³、Z=1、R=0.034 0、wR₂=0.079 9.The structure of the compounds was composed of four 1-imidazoleacetic acid and a classical Keggin[SiMo₁₂O₄₀]^4- unit and the organic ligands and the polyoxo-metalate anion formed a one-dimensional chain along x axis through electrostatic interaction,proton transfer and hydrogen bonding.These chains were parallel to each other,forming a two-dimensional layers parallel to the xy plane,which were connected by hydrogen bonds to obtain a three-dimensional network structure.The catalyst exhibited excellent catalytic activity in the oxidation of iodide ion,and the reaction rate reached 2.641 6×10^-5 mol/（L·s） at the condition of c（SiMo-12）=2.0×10^-4 mol/L、c（H₂O₂）= 2.0×10^-3 mol/L、pH=1.4、T=50 ℃,which was 1 565 times higher than that without catalyst.