Ammonia nitrogen in electrolytic manganese residue (EMR) is the main factor limiting its comprehensive utilization, and oxalic acid leaching technological can effectively remove ammonia nitrogen from EMR. In this paper, the technological conditions affecting the leaching of ammonia nitrogen from electrolytic manganese residue were studied. The material changes were characterized by FT-IR, XRD, XPS, SEM and EDS. The leaching model of ammonia nitrogen was established by kinetic analysis and thermodynamic calculation, and the leaching mechanism was discussed. The results show that when the liquid to solid ratio is 2, the amount of oxalic acid is 10% and the leaching time is 20 min, the residual concentration of ammonia nitrogen is 13.85 mg/L and the ammonia removal rate is 98%. Ammonium phosphate in electrolytic manganese residue mainly exists in the crystal lattice of insoluble calcium sulfate, oxalic acid facilitate the release of ammonium phosphate from the calcium sulfate interlattice. The leaching rate of ammonia nitrogen is controlled by chemical reaction and interfacial mass transfer mixing, and the energy release is the most and the structure is the most stable when ammonium ion and oxalic acid are coordinated 1∶1.