Abstract: Low density steels attract the attention of structural steel researchers due to their good comprehensive mechanical properties and low density characteristic. In this study,the thermodynamic equilibrium states of Fe-Mn-Al-C alloys with medium manganese and aluminum contents at different temperatures were calculated by Thermo-Calc software with TCFE 7 date base. The statistical data of phase ratio in the dual phase region were summarized and then processed by translation and correction methods to plot the Schaeffler diagram,which is applicable to design the composition and phase ratio of Fe-Mn-Al-C alloys with medium manganese and aluminum contents. Possible phases in these steels with different compositions were discussed according to the calculation of martensitic transformation temperatures. The accuracy and applicability of the Schaeffler diagram were verified by the experimental phase ratio and phase type of several typical Fe-Mn-Al-C alloys. The information of phase ratio and phase type in Fe-Mn-Al-C alloys can be obtained easily from the plotted Schaeffler phase diagram.