The electrochemical behavior of SiCuW11 heteropolyacide in acidic aqueous solution was studied. The effect of solution pH on the electrochemical behavior of SiCuW11 was discussed and the mechanism was suggested. New electrode was modified by multilayer films composed of heteropolyanion (SiCuW11) and cationic polymer poly (diallyldimethylammonium chloride). Cyclic voltammetry showed the uniform growth of the film. The modified electrodes exhibited some special electrochemical properties in the films, different from those in homogeneous aqueous solutions. The effect of pH on the redox behavior of SiCuW11 in the films was discussed in details. The multilayer film electrodes have an excellent electrocatalytic response to the reduction of BrO3- and NO2-.