Abstract: The crystal compositions of self-desulfurization residues produced in a 1 025 t/h pulverized coal fired boiler using Shenmu coal were studied, which had the self-desulfurization efficiencies of 27%～33% at the full steam load. It is found by XRD analysis that the amorphous phase content is 91.2% and the CaCO3 content is 2.1% in the feed coal. In the fly ash derived from coal combustion at the full steam load, the vitreous phase content is 70.5% and the sulfation product CaSO4 content is 3.4%, while the CaCO3 and CaO contents are 4.7% and 2.2%, respectively. In the bottom ash, the albite content is 59.2% and the vitreous phase content is 25.7%, but none of CaSO4, CaCO3 and CaO phase is detected. With a decreaseof steam load of the boiler, the vitreous phase content in fly ash decreases but that in bottom ash increases.