The invention discloses a preparation method and a use method of a manganite catalyst applied to catalytic decomposition of nitrogen oxides at a low temperature. The preparation method comprises the following steps: mixing and stirring Mn(CH3COO)2.4H2O and ethylene glycol, heating to 120 DEG C, introducing nitrogen at 120 DEG C, adding an alkaline carbonate solution, stirring for reacting for 1 hour, cooling, performing suction filtration, drying, calcining at 450-500 DEG C for 3-5 hours, tabletting, crushing, and sieving, thereby obtaining the manganite catalyst. The manganite catalyst has a regular nano spherical structure, and can be used for efficiently decomposing nitrogen oxides at a low temperature of 250-350 DEG C. The manganite catalyst has good performance of catalytic decomposition, which can be up to 63.9%, on nitrogen oxides at a low temperature.