In this research, the coke layer on the surface of ascension pipe is investigated, and X-ray fluorescence spectrometer (XRF), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR) and Laser confocal Raman spectrometer (Raman) are applied to investigate mineral composition of the coke, component structure and molecular structure of different coke layer. The research focuses on the differences of coke layer from outer surface to inner surface, and further reveals coking mechanism of ascension peipe heat exchanger. The research displays that the elements of ferrous, sulfur and chromium in dust can catalyst polycyclic aromatic hydrocarbons (anthracene, naphthalene et. al) in raw gas to form carbon particles and deposite on the surface of ascension peipe, providing carrier for tar condensation when the temperature decreases to coking temperature. All of the coke layers contain aromatic structure, and from outer surface to inner surface, the aromatic lamellas spacing (d002) gradually decreases, the value of diameter (La) firstly decreases then increases, and the stck high (Lc) and layer number (N) are stable first then increase. The graphitizing process of the coking layer is from inner layer to outer layer, and —COOH and C—O structures on the edge of the aromatic layers degrade and peel out to form highly regular conjugate structure. The C element in the coke layer is in the form of mixture of crystalline carbon and amorphous carbon. The above research provides experimental and theoretical basis for solving problems of coke and corrosion of ascension pipe, improving heat exchange efficiency, effectively recovering sensible heat of raw gas and decreasing energy consumption of coking enterprises.