Fe3O4 nanomaterials have received great attention in various technology fields. However, the limitations are Fe3O4 is easy to agglomerate and obtaining Fe3O4 nanoparticles of tunable magnetism and controllable size, and well-dispersed ability remains a challenge. In this study, a simple hydrothermal process with propanediol as the solvent was used to prepare Fe3O4 nanoparticles. In the optimization of preparation conditions, three key factors (hydrothermal temperature, hydrothermal time, and solvent volume) were optimized by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that the magnetism and the phase content of the prepared Fe3O4 were controllable during the optimization process. The optimum hydrothermal temperature was 170 ℃, hydrothermal time was 18 h and solvent volume was 40 mL. The elemental composition, surface morphology, and magnetic properties of Fe3O4 nanoparticles were characterized. The prepared Fe3O4 nanoparticles exhibited superparamagnetic properties and high crystallinity, with an average particle size of 20 nm, a specific surface area of 84.756 m2/g, a pore volume of 0.265 cm3/g, and saturation magnetization (Ms) of 129.38 emu/g.