A series of three-way catalysts was prepared by different cell density substrates with different precious metal contents and washcoat loading. Light-off characteristics of the catalysts were studied by analog computation and tested on engine bench. The results indicate that high cell density of the substrate can improve the catalyst light-off characteristics and air-fuel ratio characteristics markedly, decrease precious metals content in the catalyst and enhance the capability of purifying HCs. The light-off temperature is dependent on the synergic relationship between the substrate cell density and precious metals content. The influence of substrate cell density on air-fuel ratio characteristics is stronger than that of precious metals content. For the aged catalyst, the precious metals content is still an important factor for maintaining catalytic conversion