Abstract: The relationship between surface acidity and pore structure of mordenite was investigated by FT-IR of binary basic nitrogen compounds displacement, BET and pore size distribution calculated using MP method. The distribution, surface state and interaction of palladium on mordenite were studied by XPS. It is shown that large number of irregular framework and secondary pore will emerge on the surface of mordenite as its dealuminized extent increases. The stronger Bronsted acid site is mainly distributed on the external surface, the more palladium exists on the surface of mordenite. An isomerization of light paraffin is promoted by the interaction between palladium and Bronsted acid site on external surface of mordenite.