Abstract: In order to study the changes of sulfur and calcium elements when oil cracking in carbonate reservoirs, collecting Ordovician Yingshan formation oil of well TK772 in Tahe Oilfield, through semi-open test system "formation porosity thermocompression simulation experiment instrument" to carry out gas generating simulation experiments in the formation conditions, using synchrotron radiation technology "X-ray absorption near edge structure" to detect the chemical mode of sulfur and calcium elements in solid products. The results showed that sulfur compounds in solid products of crude oil direct lysis (crude oil limestone(Series 1)) are the thiophene and calcium sulfate, is the result of the oxidized of thiophene substances in crude oil; the calcium-containing compound calcium is carbonate-based. The presence of dissolved sulfate crude lysate (crude oil limestone magnesium sulfate(series 2)), sulfur-containing compound is a solid product calcium sulfate-based and supplemented thiophenes, may be result of the dissolved sulfate (magnesium sulphate) , TSR and dissolution - precipitation. Accompanied by elevated temperature and pressure in series 2, H2S generation and calcium sulfate relative percentage increase, indicating the occurrence of thermochemical sulfate reduction (TSR) in crude oil cracking process; calcium sulphate formation and enrichment shows, acidic fluid generated during TSR in carbonate reservoirs can produce significant dissolution, and secondary gypsum may be generated.