Abstract: The influence of alkaline-earth metal oxide on the catalytic properties of manganese-rare earth metal oxides system has been studied. When a small amount of alkaline-earth metal oxides is added, the thermostability of the catalyst can be improved. The sequence of thermal resistance is CaO > SrO > BaO. It has been found that initial activity and thermal stability of a catalyst are satisfactory when its BaO content is 1.0%. Test results also show that the influence of alkaline-earth metal oxide on the catalytic properties is probably through the action of its surface acidity or basicity. The appropriate acidity of catalyst is about 0.4mmol/g.