Abstract: One coal and two representative fly ashes from the Shell gasification process were used in the study. One fly ash was the captured fly ash, and the other was taken from the heat exchanger. The particle size distribution, chemical composition, surface morphology of samples were studied by laser particle analyzer, X-ray fluorescence spectrometer and scanning electron microscopy respectively to explore the mechanisms of adhesion. The enrichment coefficient was used to describe the element migration from the coal to the fly ash. The results show that the formation of iron-bearing minerals and the enrichment of Na, K, Fe, S, P especially the enrichment of Na and Fe on the surface of fly ash particles are the main factors on the adhesion.