The (computer designed shape) CDS type of PdAg/Al2O3 catalyst in single-stage reactor provides superior catalytic activity and selectivity of ethylene in comparison with those of existed two-stage reactors packed with G-58B catalyst under industrial operating conditions. In this research, the contents of palladium and silver of catalysts were analyzed by inductive coupling plasma (ICP). The X-ray photoelectron spectroscopy (XPS) showed that Pd-Ag alloy has been formed. Higher yield of ethylene may be interpreted by both geometric and electronic effect induced from silver metal. By means of Pyrolysis/GC/MS analysis of used catalysts, the components of carbonaceous deposits were found to be n-alkenes, including n-C8 similar to n-C16 or n-C1 8, which may result from oligomerization of acetylene.