Abstract: Coke deposits on Pt-Sn/Al_2O_3 reforming catalysts and those on the wall surface of the reactors were studied by using TGA, TPO, XRD, HNMR, C-C-MS, SEM and TEM tests. Great differences between these two kinds of coke deposited was observed in their morphological aspects, structures, compositions and properties. Experimental results revealed that different mechanism of carbon deposition on the wall surface of the reactors and on the surface of catalysts would be envisaged.