Multi-modal nuclear fission of fermium isotopes at low excitation energy is dynamically investigated. The multidimensional Langevin equation is used for the dynamical calculation. We use the potential energy taking account of the microscopic energy which depends on the excitation energy. We calculate the mass and the total kinetic energy (TKE) distributions of the fission fragments for ²⁶⁴Fm. The deformation of the fission fragments at the scission plays an important role in classifying the nuclear fission modes. We show that there exist following three types for the scission configuration classified by the shape of the fission fragments: mass-symmetric compact configuration, mass-asymmetric configuration, and mass-symmetric elongated configuration. We calculate the average mass number and the average TKE for each configuration. We also study the isotope dependence of the mass distribution of the fission fragments from three fermium isotopes.