In this paper, a DFT calculation was used to demonstrate the catalytic role of a WOX/SiO2 catalyst and show the excellent performance in 2,5-dimethylfuran to para-xylene conversion. A model of highly dispersed tungsten oxide supported on the amorphous silica was firstly constructed. A periodic DFT calculation was thereafter carried out to determine the reaction pathway, transition state (TS) and important intermediate structures. For reference purpose, the calculation was also repeat on an alkali ion, representative of a Lewis acid catalyst. Unexpectedly and although tungsten oxide is generally considered and characterized to be a Lewis acid, its mechanism for catalyzing the conversion of 2,5-dimethylfuran and ethylene to PX is differs significantly from other Lewis acids like alkali metal. Typical epoxide intermediates observed in other Lewis acid catalyzed systems are not formed over a WOX/SiO2 catalyst. The calculated reaction barrier indicated that the WOX/SiO2 catalyst has no obvious catalytic effect on the Diels-Alder cycloaddition for 2,5-dimethylfuran and ethylene. It mainly accelerates the dehydration step. The reason for the unique catalytic mechanism of WOX/SiO2 catalyst relies on the coordination of 2,5-dimethylfuran and tungsten that leads to the Diels-Alder cycloaddition that follow the so-called inverse electron demand mechanism. A new catalyst for this reaction was proposed based on the obtained mechanistic understanding. Graphic