A series of magnetic hollow Fe3O4 nanospheres were synthesized by hydrothermal method, and the different methods in the synthesis process were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and hysteresis loop. The influence of molecular weight polyethylene glycol (PEG400、1000、4000) and its addition amount on the particle size, magnetic properties and sedimentation properties of Fe3O4 microspheres. The study found that when the molecular weight of polyethylene glycol is the same, the magnetic Fe3O4 hollow nanospheres obtained by adding 0.6g polyethylene glycol have better dispersibility in water and organic solvent DMAc than 0.3g polyethylene glycol. The resulting microspheres for particle size is larger and the magnetic properties are similar. Compared with the amount of polyethylene glycol added, the molecular weight of polyethylene glycol has a greater impact on the magnetic properties of the magnetic Fe3O4 hollow nanospheres. The particle size of the magnetic Fe3O4 hollow nanospheres can be adjusted by changing the molecular weight of polyethylene glycol. The particle size of the magnetic Fe3O4 hollow nanospheres has a decreasing trend with the increase of the molecular weight of polyethylene glycol. The magnetic Fe3O4 hollow nanospheres obtained by adjusting polyethylene glycol have good dispersibility in water and organic solvent dimethylacetamide (DMAc), especially in water solvent for 8 days to completely settle, add 0.6g The magnetic hollow Fe3O4 nanospheres obtained by PEG4000 have outstanding dispersibility in DMAc, and are expected to be well applied in the fields of wastewater treatment and electromagnetic wave absorption.