A series of complex oxide La _{1 - x}S r _x Co _{0. 5}Mn _{0. 5}O ₃ perovskite - type catalysts in which La ³⁺ is partly substituted for S r ²⁺ were synthesized at low temperature through a combustion process and the catalysts were characterized by XRD, IR and BET. The activity of the catalysts for simultaneous removal of NO _x and diesel soot particulates were examined in details using temperature programmed reaction (TPR) technique. The results show that after partial substitution of La ^{3 +} with Sr ²⁺ the oxygen vacancy concentration increases significantly , B ^{3 +} - B ^{4 +} system is formed and consequently the catalytic activity for simultaneo us removal of NO _x and diesel soot particulates is significantly improved. It is found through catalytic property testing that catalytic activity is best when x =0. 4 and the catalyst and the soot is mixtured tightly , temperature of soot combustion is 305 ～ 435 ℃, the conversion rate of NO _x can reach to 43. 7%.