Deformation-induced martensitic transformations (DIMTs) have been widely observed in iron and ferroalloys under various mechanical loading conditions, thereby showing extreme scientific merits and engineering significance. Since deformations and fractures affect one another and reflect the relative movements of atoms, DIMTs often accompany fractures. In this work, molecular dynamics simulation was performed with a (010) [100] pre-cracked model to study DIMTs from an a-Fe single crystal during the mode-I fracture process. The observed DIMTs were verified using first-principle calculations. A crack tip tracking algorithm by scanning the nearby atoms is proposed, and the obtained critical stress intensity factor was proved to be close to the experimental results. Quasi-cleavage fracture happened with the nucleation and growth of the c (fcc) phase, which was transformed by activating the {121} h111i and {110} h111i shears near the crack tip. The layered e (hcp) phase was formed by stacking faults inside the c phase and was unstable by driving force analysis.