Coal is a major pillar of our national energy，however，the SO2 and other pollutants released by coal combustion have caused serious damage to the environment. The organic sulfur in coal has a complex structure and diverse forms so that the research is relatively difficult. Therefore，the research on the conversion characteristics of organic sulfur in coal can provide theoretical support for the control of SO2 pollutant emissions and achieve clean coal combustion. In order to study the conversion of organic sulfur forms in coal during the preheating process，a preheating combustion test of Shenmu bituminous coal was carried out on a 30 kW preheating combustion experiment platform. During the experiment，solid samples were taken at the measurement points，and X-ray photoelectron spectroscopy technology（XPS)and diffraction of X-rays（XRD)was used to analyze Shenmu bituminous coal and preheated semi-coke. The results show that the main forms of organic sulfur in Shenmu bituminous coal can be divided into four types:mercaptans and thioethers（32.6%)，thiophenes（16.0%)，sulfoxides（15.9%)and sulfones（15.3%). Inorganic sulfur includes CaSO4 ，FeS2. When the preheating temperature reaches above 800 ℃，the sulfur form and content in the preheated semi-coke change greatly compared with that in the raw coal. The inorganic sulfur in the preheated semi-coke has CaS in addition to the original types. The degree of decomposition of organic sulfur in preheated semi-coke increases with the increase in air equivalent ratio during preheating，among which mercaptans and sulfides are reduced the most due to decomposition，followed by thiophenes and sulfoxides，and the relative content of sulfones increases. The reason of the sulfones increasing is from two aspects，one is due to the discompose of other substance like mercaptans or thiophenes，and the other is due to the conversion from mercaptans to sulfones.