Nanobainite layer was prepared by laser hardening combined with isothermal transformation (LHCIT) at 250°C, which between M_s and M_d temperature. The microstructures of the nanobainite layer were analyzed by X-ray Diffraction (XRD) and transmission electron microscope (TEM). The nanohardness of the nanobainite layer were measured by the nano-mechanical tester. The results show that the residual stress value of the laser hardening layer is 319.15 ± 21.05 MPa, and the shear band such as stacking fault bundle, nano-twin and ε-martensite can be formed by the stress in austenite during LHCIT. The highest nano-indentation hardness of the nanobainite layer is 8.81 GPa and the average nanohardness of the nanobainite layer is evidently increased from 6.65 GPa to 7.76 GPa. The reduced hardness is bimodal in the laser hardening layer, and it is demonstrate that the high hardness of the nanobainite layer can be obtained by the formation of the shear band.