The reaction between hydrogen and organic sulfur in semi-coke at high temperature was studied in this paper.Crashed and sieved semi-coke sample (with particle size of 15 μm) was placed in 5 g batches in a 22 mm I.D. differential reactor.The release of hydrogen sulfide at run temperature and under different hydrogen atmospheres was followed by hydrogen sulfide detector.The residual was analysed for sulfur.Results showed that the desulfurization of organic sulfur in semi-coke powder could be described much better with the random pore model than with grain reaction model.Grain reaction model is only adapted to the initial stage of organic sulfur removal from semi-coke powder under hydrogen atmosphere while the random pore model is adequate for the whole stage.Experiment and theoretical study also disclosed the possibility of transformation of organic sulfur to heterocyclic organic compounds such as thiophene.