The invention discloses a preparation method of Fe3O4 nanomaterial with controllable morphology, and relates to the technical field of nano functional materials. The method aims at the shortcomings ofthe existing Fe3O4 nanomaterial in the method for preparing a special morphology, such as adding a surfactant. The method provides a self-assembly preparation method controlled by urea. The continuous morphology between the nanoparticles, the nanosheets and the nanoflowers can be controlled by the ratio of urea addition and the reflux reaction time. The particle size is 1 to 3.5Mum with good dispersibility, which can be dispersed in water; the material has good magnetic properties and has no hysteresis, no remanence and no coercive magnetic field at room temperature. Since the saturation magnetization is 60-80emu/g, the material can be separated by an ordinary magnet and exhibits superparamagnetism at normal temperature.