To obtain the valuable p-xylene from biomass with a high selectivity, several transition non-noble metals as main components of catalysts for aromatization of diisobutylene were explored. A volcano curve with the top marked by Cr(3d⁵4s¹) could be found between the activity and the atomic outer-shell electrons number of transition metals. The further addition of alkaline earth metal showed that the modification of surface properties by Mg doping could improve the catalytic performance. With Cr–Mg–Al–O as catalysts, the enhanced selectivity and single pass yield for the p-xylene formation could be obtained. Meanwhile, the side reaction of cracking could be suppressed, which might be attributed to the increment of the weak/strong acid ratio by Mg addition. Moreover, the catalysts kept a stable catalytic performance in the regeneration and reuse cycles.