Effects of temperature on coke and its precursors formation were studied during catalytic cracking of toluene over USY catalyst. The coke and its precursors were analyzed by TGA, solid-state ¹³C NMR，elemental analysis, GC-MS and temperature-programmed oxidation(TPO). The coke deposited on the catalyst is mainly composed of polyaromatic hydrocarbons (PAH). It reveales that the total amount of coke and the yield of PAH and its ring numbers in liquid phase increase with the increase of cracking temperature. It concludes that high temperature is bad for coke inhibition.