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The solid products of pyrite decomposition during coal pyrolysis under nitrogen atmosphere at different temperatures were investigated by X-ray diffraction (XRD), and the solubilities of the corresponding compounds in hydrochloric acid and nitric acid were examined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The feasibility of using the standard method for sulfur forms analysis of coal to determine the sulfur forms in char was discussed. It is found that the standard method is unsuitable to analyze the sulfur forms of the char and big error is introduced during calculation of the organic sulfur in char. During pyrolysis, pyrite (FeS2) is converted to pyrrhotite (Fe1–x S) and/or ferrous sulfide (FeS), which dissolve in HCl solution and lead to an elevated value of organic sulfur determined by the standard method. A modified calculation method of sulfur forms in char is recommended. The organic sulfur content in pyrolysis char obtained by this method is much lower and more accurate than that obtained by the standard one. The modified method for the sulfur form analysis of char is superior to the standard one, especially for the chars obtained from coals with high pyrite content and pyrolyzed at high temperatures.