A novel Micro-Reactor-GC system was used to study the performance of two kinds of FCC catalysts coked in a FFB reactor under simulated industrial conditions using dodecane and octene as probe molecules. The result shows that the performance of the two cokedcatalysts differed significantly. The 129Xe NMR technique was used to detect the location of coke deposition on the catalysts, which gave a good explanation of the experimental results.