Abstract: Two coking coals with high organic sulfur were separated into five fractions with different density ranges by heavy medium separation. The occurrences and transformation of sulfur during pyrolysis of different fractions were investigated by X-ray photoelectron spectroscopy (XPS), solid state ¹³C nuclear magnetic resonance (¹³C NMR) and pyrolysis mass spectrometry (Py-MS). The results show that different fractions have significant differences in distribution, occurrence, and chemical environment of sulfur. Organic sulfur is mainly distributed in the low density fraction (D1) and exists in the form of thiophene. Inorganic sulfur such as mineral component is mainly distributed in the high density fraction (D5). As the increase of density of coal fraction, the proportion of aliphatic carbon decreases, and aromatic carbon increases, as well as content of mercaptan and thioether in D1 increases greatly. The volatiles are greatly released since decomposition of aliphatic carbon structure during pyrolysis, which promotes the release of sulfur containing gases, and then improves desulfurization efficiency of D1. However, transformation of sulfur is mainly affected by minerals during D5 pyrolysis.