Diesel engines have been more and more widely used in heavy duty vehicles because of high efficiency and low fuel consumption compared with petrol engines. Taking ZrO₂ as the modified additive, the influence of the mass ratio of ZrO₂ and Al₂O₃ on catalytic performance was studied. The results show that, with an increase of ZrO₂ doping, the Pt particles becomes smaller at first and then larger in the catalyst. The interaction between Pt and the carrier increases and then decreases. Analysis of the activity data shows the optimized doping amount of ZrO₂ is 40 wt%, the CO/C₃H₆ complete oxidation temperatures reduced by 20 _oC and 25 _oC, respectively. The study shows that, when the ZrO₂/Al₂O₃ mass ratio in the carrier is varied, the precious metal dispersion on the catalyst and the precious metals interaction with the carrier are different with varying levels. The smaller the Pt particle size, the stronger the interaction between precious metal and the carrier, which indicates that the performance of catalyst is higher.