Spatially resolved photoemission electron microscopy (PEEM) was employed to investigate the adsorption, diffusion, and reactivity of oxygen on a defective Pd(100) surface. The defective region on Pd(100) exposed several different planes with low indexes, for example, (110) and (111) planes. Upon oxygen adsorption, various types of oxygen species formed on each plane; which behaved with different reactivities toward CO. An obvious coupling between the Pd(110) plane and its adjacent planes was monitored by PEEM during CO + O-ad reaction and resulted in the appearance of the reaction-diffusion waves on the Pd(110) plane. The occurrence of reaction coupling had a great influence on the catalytic kinetics of the crystal planes involved. However, during isothermal desorption of adsorbed oxygen on the planes, no coupling existed between adjacent planes, which implied that the reaction played a key role in the occurrence of coupling.