The dynamic tensile behavior of Fe-15Mn-3Al-0.23C TRIP/TWIP steel was studied at intermediate strain rates in the range of 7–700 s−1. The results showed that transformation induced plasticity (TRIP) effect, twinning induced plasticity (TWIP) effect, dislocation glide and adiabatic temperature rise effect coexisted during dynamic deformation. With the increase of strain rate from 7 to 70 s−1, the number of deformation twins increased and some intersecting twins appeared. However, when the strain rate approached 700 s−1, the amount of deformation twins were decreased and intersecting twins disappeared. During deformation at strain rates from 7 to 700 s−1, the strain rate had no significant effect on TRIP effect, and deformation twinning was the main deformation mechanism. The ultimate tensile strength (UTS) showed a positive strain rate sensitivity with increased strain rate, and the experimental steel exhibited remarkable mechanical properties with the product of ultimate tensile strength and total elongation (PSE) of 61.5 GPa% at the strain rate of 70 s−1.