NH3-reducing desulfurization was demonstrated using a high-sulfur coke calcining desulfurization experiment at 1000 degrees C, and the sulfur chemical reactions of the three aromaticities of thiophene were studied during desulfurization. Results showed that NH3-reducing desulfurization could significantly remove sulfur in the coke, and the best operation temperature was approximately 800 degrees C, at which more than 80% of organic sulfur could be removed. The physical and chemical indicators of petroleum coke after desulfurization were not affected. Thermodynamic calculation results showed that the desulfurization reaction was more favorable at higher temperatures. However, the reaction was also affected by other factors; thus, the desulfurization efficiency decreased when the desulfurization temperature exceeded 800 degrees C. This paper presents a specific explanation of this phenomenon.