The use of high-sulfur petroleum coke (petcoke) as raw material in the carbon industry requires an effective desulfurization process. Hydrodesulfurization (HDS) and NH3 gaseous desulfurization are the most effective approaches. However, the S/N removal and the gasification ability of HDS and NH3 desulfurization have not been well-explored. Here, petcoke transitions were examined using the reactive force field simulation approach at a constant volume and temperature (3000 K for 250 ps). The S/N removal and transformations in HDS were thiophenic S -> C1-4S, H1-2S -> H2S, and pyrrolic and pyridinic N -> C1-4N -> HCN. Given the large H2 production from NH3 decomposition, the S/N removal and transformations in NH3 desulfurization were similar to those of HDS. However, NH compounds (NH3) directly bonded with C atoms in petcoke, adding to the coke yield but adding an additional heteroatom challenge with utilization after NH3 desulfurization. Produced C1-4N (CN, mostly) and H2 were transformed into HxC1-4N (0 < x < 5). The final stable gaseous compounds were HCN and H2S. For NH3 treatment, some NH compounds bonded with C atoms, resulting in an increased N content after NH3 desulfurization (higher coke yield compared to HDS).