Abstract: The Mg-Al hydrotalcites used as the support were prepared by precipitation method, and then the catalysts with different amount of doped potassium, (xK/MgAlO) were prepared by impregnation method. The effects of K on the structure and catalytic activity of the xK/MgAlO catalyst were investigated in SO₂ containing gases. The key mechanism of K-doped (xK/MgAlO) catalysts to reduce the soot ignition temperature during the reaction was illustrated. The differences of the crystal structure between calcined and uncalcined Mg-Al hydrotalcite were studied by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and the transient response method. The experimental results showed that the 3R layered structure of Mg-Al hydrotalcite disappeared while the spinel phase appeared, and the layered structure collapsed into spherical particles after calcination. Potassium doping formed more oxygen vacancies that are conducive to the combustion of diesel soot, decreased the temperature of soot combustion from 380 to 253℃ though in SO₂ atmosphere and significantly enhanced the conversion efficiency of NO_x.