Abstract: The soluble coke in deactive zeolite catalyst was characterized using capillary column GC/ITD (Ion Trap Detector)technique. The zeolite was dissolved with a solution of hydrofluoric acid at 40％ when treating the coked zeolite at room temperature to liberate the inner "coke". About thirty polycyclic aromatic hydrocarbon compounds were identified in experiment result. It was proved that the soluble coke is the precursor of coke in the coking processing of zeolite catalyst.