Abstract: The mechanical properties and strengthening mechanism of Fe-24Mn-3Si-3Al TWIP steels were investigated as a function of annealing process. The microstructures of the samples were analyzed by transmission electron microscopy, scanning electron microscopy, energy disperse spectroscopy. The experimental results indicate that as the annealing temperature and the holding time change, the mechanical properties of TWIP steel do not rise or fall monotonously, as would be conventionally. The mechanical properties change in the annealing processes of annealing temperature 800℃ for 10 min and 900℃ for 20 min. The strengthening mechanism is mainly dispersion strengthening in the case of annealing process of 800℃ annealing temperature for 10 min, and an increase in the precipitation of (Fe, Mn)₂₃C₆ leads to better mechanical properties. However, in the case of annealing process of 900℃ for 20 min, the precipitation of (Fe, Mn)₂₃C₆ does not change obviously, but many twinning systems are initiated and secondary twin and twin delivery are observed, which result in an increase in the ultimate tensile strength.