A preparation method of perovskite catalyst, represented by the following Chemical Formula 1: LaxAg(1-x)MnO3 (0.1≦x≦0.9), includes the steps of 1) preparing a metal precursor solution including a lanthanum metal precursor, a manganese metal precursor and a silver metal precursor, 2) adding maleic or citric acid to the metal precursor solution, 3) drying the mixture separately several times with sequentially elevating the temperature in the range of 160 to 210° C., and 4) calcining the dried mixture at 600 to 900° C. for 3 hours to 7 hours.