A semi-empirical relationship has been established between the shape memory effect (SME) of Fe-Mn-Si based alloys and its influencing factors such as strengthening effect (characterized by tau(o), the c.r.s,s. of perfect dislocation slips), grain size (R), prestrain (e), stacking fault energy (or probability of stacking fault (P-sf) and training cycle number (n). It is indicated that high P-sf, tau(o) and small R are beneficial for achieving a good SME and training is still necessary, which is consistent with the previous experimental results. It also provides a theoretical reference for designing new shape memory alloys.