The magnetite polybutyl acrylate(PBA)/Fe₃O₄ composites were prepared for absorbing oil by precipitation polymerization in supercritical carbon dioxide (scCO₂). At first, the oleic acid-coated Fe₃O₄ nanoparticles were synthesized by chemical co-precipitation. Then the magnetite PBA/Fe₃O₄ composites were prepared by using the monomer BA, initiator AIBN, cross-linker EGDMA and cosolvent n-hexane. The morphology and structures of PBA/Fe₃O₄ composites were characterized through Fourier transform infrared spectroscopy (FT-IR), transmission scanning electron (TEM). Furthermore, their thermal stability, magnetic properties and oil absorption ability were evaluated. The results show that the PBA/Fe₃O₄ (6.7%) composite obtained at 17 MPa could absorb diesel oil up to 7.0 times of particles mass. In addition, the PBA/Fe₃O₄ composites could be recycled by using magnet. After cycling ten times, the absorption performance of the composite is remained above 5 g/g, which show an excellent reusability.