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Electric furnace nickel-iron slag is characterized by high magnesium, in this paper, HCl was used as leaching solution to recover magnesium in nickel-iron slag to prepare MgCl2·6 H2O for molding magnesium oxychloride cement (MOC). The orthogonal experimental method was used to obtain the optimal leaching system of Mg2+ in nickel-iron slag and the optimal mix ratio of nickel-iron slag-based magnesium oxychloride cement (PMOC). PMOC and analytically pure magnesium chloride hexahydrate-based magnesium oxychloride cement (RMOC) were molded under this ratio. It was found that the 28d strength of PMOC prepared with the same ratio was higher than the 28d strength of RMOC and more stable, and the water resistance of PMOC was also improved. The hydration products of both specimens were characterized by x-ray diffraction (XRD), thermogravimetric (TG), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The hydration products of MOC were found to be 5-phase and Mg(OH)2, and it was found that the higher strength of PMOC in the same ratio was due to the higher content of 5-phase in PMOC than that of RMOC, and the lower content of Mg(OH)2 than that of RMOC. It was found that the content of Mg(OH)2 was lower than that of RMOC in PMOC after 7 d of soaking, which was the reason why the strength and water resistance of PMOC were slightly better than that of RMOC after soaking.