Keggin-type polyoxometalates (PMo11V) and reduced graphene oxide (rGO) are used as two building blocks to fabricate a nanocomposite film via layer-by-layer self-assembly method. The composite film is characterized by UV-vis absorption spectra (UV-vis), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The composite film shows high electrocatalytic oxidation of nitrite, the linear response range from 0.125-1160 mu M and the detection limit is 0.0028 mu M (S/N = 3), which is explored by amperometric method. The high performance of the composite film is due to the combination of the advantages of PMo11V and rGO. Moreover, the electrochemical experiment results indicate that the proposed sensor exhibits excellent selectivity, good reproducibility and long-term stability, as well as satisfactory practical ability in mineral water, milk and tap water.