The Pd/Al2O3 close-coupled catalysts supported on modified alumina were prepared by the impregnation method, and characterized by means of H2-temperature programmed reduction (H2-TPR), CO chemisorption, and X-ray photoelectron spectroscopy (XPS). Both total catalytic activity and single reactions in related to C3H8 conversion were tested in simulated exhaust gas. The results show that the amount of active PdOx decreases and negative metallic Pd0 generates during aging treatment. The light-off temperature (T50) and complete conversion temperature (T90) increase by 76 oC and 64 oC after aging treatment, signifying that the low-temperature activity decreases more obviously than high temperature property. The results of comparison among single reactions indicate that the light-off activity of reactions which occur in atmosphere with the participation of NO but without H2O injection decrease dramatically after the aging treatment. The inhibitive effect of NO on light-off activity and the positive effect of H2O on high temperature property become obviously during the aging treatment.