Abstract: Nano-Fe3O4 particles were prepared by oxidative precipitation together with weak exterior magnetic field induction. The crystalline form，morphology and magnetic properties of the prepared particles were characterized by using XRD，SEM and VSM. The introduction of a weak magnetic field could accelerate the phase transformation of goethite (α-FeOOH) to magnetite (Fe3O4). The prepared nano-Fe3O4 particles have a spinel structure and are well crystallized. Induced by the weak magnetic field，the particles tend to be formed with a polyhedron morphology with a narrower particle size distribution and a larger diameter. Due to the changes in crystallinity，morphology and size distribution，the prepared nano-Fe3O4 particles have a higher saturation magnetization and a stronger coercive force.