The influence mechanism of SO₂ on the NO_x removal performance of a La_0.9Sr_0.1Mn_0.97Pd_0.03O₃ catalyst was investigated in this paper using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and the transient response method. Results show that incorporating the noble metal Pd into the catalyst increases the specific surface area of the original catalyst, creating a suitable place for NO_x contact, reducing the ignition temperature of soot and improving the NO_x, C₃H₆ and CO conversion of the catalyst effectively. Although the catalyst La_0.9Sr_0.1Mn_0.97Pd_0.03O₃ forms a stable and irreversible sulphate after reacting in a high concentration of SO₂ (300 ppm) atmosphere, it retains a high removal efficiency of NO_x.