A non-aqueous phase (Sb/Fe/NMP) desulfurization system for the removal of hydrogen sulfide from natural gas was constructed by introducing SbCl3 and FeCl3 in a specific ratio into N-methylpyrrolidone (NMP). The desulfurizing agent and its sulfur product were characterized, and the absorption pattern of H2S by the system was investigated by static desulfurization experiments. The results indicate that the desulfurizer’s sulfur capacity can reach 16 g/L at room temperature and pressure, and that adding the optimum amount of water and appropriate temperature increase can assist to increase desulfurization efficiency. The system maintained a sulfur capacity level of more than 90% of the initial sulfur capacity after five consecutive desulfurization-regeneration cycles. XRD and XPS spectrogram revealed that the regenerated solid product was high purity sulfur. Sb3+ is a key component to ensure the effective absorption of H2S. The presence of a moderate amount of Fe3+ can oxidize and absorb small amounts of H2S and promote the oxidative regeneration of the system. In addition, we combined the obtained experimental data with density flooding theory (DFT) theoretical calculations to show that the effective coordination of Sb(III) with HS- in the NMP environment is the main reason for the effective absorption of H2S by the desulfurizer. NMP is not involved in the coordination absorption process of hydrogen sulfide.