Abstract: The effect of pressure on coke and its precursor's formation was studied during catalytic cracking of toluene over USY catalyst. The coke and its precursors were characterized by TGA, FTIR, solidstate 13C NMR，elemental analysis, GCMS, and temperatureprogrammed oxidation (TPO) analysis. The results indicate that coke deposited on the catalyst is mainly composed of polyaromatic hydrocarbons (PAHs). It reveals that the total amount of coke decreases, whereas the number of the rings of PAHs and yields of PAHs in the liquid phase increase with increasing cracking pressure. It is concluded that supercritical fluid plays an important role in extracting coke precursors during catalytic cracking.Finally, the mechanism of coke formation was proposed.