The three-way catalyst with different cell shape substrates was prepared by the different washcoat loadings. Its catalyst’s light-off characteristics were investigated by the simulating calculation and the engine bench experiment. The experimental results showed that, heat transfer coefficient (Hs) couldn’t be improved by the increase of coating rate, in contrast heat transfer coefficient (Hs) and the catalytic conversion decreased when the coating rate was more than 45%. Therefore, it had some negative effects on the light-off characteristics and air-fuel ratio property. The calculation analyses and the engine bench experiment also proved that the best coating rate was 45% for the substrate of 400cpsi.