Abstract: A series of modified FER zeolite samples with different acid types, acid density and accessibility were prepared by using different concentrations of ammonium hexafluorosilicate (AHFS) for isomorphous substitution. The texture properties were characterized by XRD and N₂ adsorption isotherms. And the acid properties were characterized by NH₃-TPD and Py-FTIR. The results showed that when 1-butene and isobutene were respectively used as raw materials, the optimal reaction temperature for skeleton isomerization was 350 ℃, and the side reaction was more obvious when isobutene was used as raw material. During the dealumination process, two new Lewis acid sites with different strength were generated, due to the interaction between the dealumination agent and the extra framework aluminum hydroxyl species on the zeolite. During the reaction, the above two Lewis acid sites promoted the oligomerization-cracking of isobutene, thereby, reducing the selectivity of the main reaction.