Abstract: A layer of manganese dioxide/poly (p-phenylenediamine) (PoPD) complex was coated on the surface of polyphenylene sulfide (PPS). First, the o-phenylenediamine (OPD) monomer was uniformly adsorbed on the surface of the PPS fiber by the effect of π-π conjugation. Then, the o-phenylenediamine was oxidized by the potassium permanganate solution to produce poly (p-phenylenediamine) coat, while the potassium permanganate was reduced to MnO₂ catalyst and inserted into the poly (o-phenylenediamine) matrix. The MnO₂ catalyst was firmly bonded with the PPS filter because the MnO₂/PoPD complex formed by in-situ polymerization exhibited a strong bond with the PPS filter. The preparation method of MnO₂/PoPD@PPS composite filter was simple. Due to the mild experimental conditions, the performance of the PPS filter media was not damaged. The structure and properties of MnO₂/PoPD@PPS composite filter were studied in detail by FESEM, XPS, XRD, FT-IR and denitrification test. The results of denitration test show that the denitrification rate of MnO₂/PoPD@PPS composite filter increases with the increase of KMnO₄/PPS mass ratio. The optimum denitrification rate is 36%-94% at 80-180℃ with the KMnO₄/PPS mass ratio of 1:1, and it is 88% at 160℃ after 10 h catalyst stability test. The XPS spectrum of Mn 2p proves that the catalyst on the composite filter is MnO₂ that possesses amorphous structure observed from XRD patterns. It can be observed from the FESEM diagram that the dispersion of the MnO₂ catalyst on the PPS filter is uniform.