Abstract: The microstructure and mechanical properties of Fe-8.3Mn-xAl-1C medium manganese low density steel with different Al content were studied by phase diagram calculation combined with OM, SEM and XRD. The results show that with the increase of Al content, the proportion of ferrite in the phase diagram of Fe-8.3Mn-xAl-1C low density steel increases,while the proportion of austenite decreases in the same temperature range. When the Al content increases from 9.5Al to 14.5Al, the ferrite and austenite in the steels gradually change from a reticulate distribution to a strip-like distribution along the rolling direction, the change in microstructure affects the mechanical properties of the experimental steel. The tensile strength of 9.5Al steel is 1112 MPa, the elongation rate is 12.8%, the product of strength and plasticity reaches 14233 MPa·%, and the strength is high while having good plasticity. The strength of 12.5Al steel increases to 1246 MPa, but the plasticity reduces to9.4%. The strength and plasticity of 14.5Al steel are both poor at only 924 MPa and 6.4%.