The spinodal composition zone in Al added Fe-Mn-Al-C twinning-induced plasticity (TWIP) steels can be determined by contents of Al and C and aging temperature together, based on the thermodynamic analysis. Precipitation of ordered (FeMn)3AlC carbide by the mechanism of spinodal decomposition occurs in the C-rich and Al-rich zone with low aging temperature. Increase of aging temperature shrinks spinodal composition zone to the high Al and C contents. As a result, the precipitation of (FeMn)3AlC carbide alters from spinodal decomposition to classical nucleation-growth manner gradually. Further calculation indicates that the diffusion of Al can play a key role in determining the growth rate of (FeMn)3AlC carbide at high aging temperature. © 2016, Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg.