The catalytic activities of Co3O4, Sr(NO3)(2), Co-Sr, and Co-Sr-K catalysts were studied, and the effect of the contact mode on the soot onset ignition temperature and soot oxidation rate was also discussed. All the catalysts were characterized by X-ray diffraction and thermogravimetry/differential scanning calorimetry. The catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The soot onset ignition temperature is 370 degrees C for Co-Sr catalysts with molar ratios of 1:1 and 2:1, which is the same as that of pure Co3O4. The Co-Sr catalysts containing KNO3 can greatly lower the soot onset ignition temperature. The catalytic activity of pure Co3O4 and Sr(NO3)(2) is affected by catalysts-soot contact intensity, which has nearly no effect on the soot onset ignition temperature and soot oxidation rate for Co-Sr catalysts with appropriate ratios. The cooperation of Co3O4 and Sr(NO3)(2) can accelerate the soot oxidation rate and reduce the effect of the soot-catalyst contact mode on catalytic activity. The soot onset ignition temperature is not affected by contact intensity for the catalysts with proper Co-Sr-K ratios, which shows that the cooperation of Co3O4, Sr(NO3)(2), and KNO3 can lower the soot onset ignition temperature whether in the tight contact mode or in the loose contact mode. The soot oxidation rate is greatly accelerated when the Co-Sr-K catalysts and soot are in the tight contact mode.