A novel synthesis approach is developed to prepare nanocrystalline γ'-Fe4N in this paper. High energy cryomilling approach in liquid nitrogen is used to prepare the sample. A FexN amorphous state with a degree of metastable supersaturation of N into Fe is obtained. The crystalline size after higher energy cryomilling approach is characterized to be 40 ∼ 80 nm. A post-annealing among 200 ∼ 300 °C for 10 minutes results in phase transformation from α-iron into γ'-Fe4N. Its magnetic properties and structures are characterized, showing good soft magnetic material with ultralow coercivity (0.7 Oe). It shows high electrical resistivity (375 μΩ·m) at room temperature. The feasibility of the ball milling synthesis approach in liquid nitrogen is verified, suggesting a novel approach for the soft magnetic material preparation.