Using the method of chemical co-precipitation，the super paramagnetic nanoparticles with the key component of Fe3O4 were synthesized.The magnetic beads reacted with the silane coupling agent 3-aminopropyl triethoxysilane and connected with amino groups.After activated by the agent glutaraldehyde，the magnetic beads took along the aldehyde group and coupled with aflatoxin B1 polyclonal antibody to form the immune magnetic beads.A method was established to detect the aflatoxin B1 in vegetable oil by using the organic solvent for preliminary extraction，the aflatoxin B1 immune magnetic beads system to purification and HPLC to quantification.The method showed a good linearity in the range of 5-50 μg/L with correlation coefficient of 0.999 4 and detection limit of 0.5 μg/L.The average recovery was up to 96% and the RSD was 12.5%.With the advantages of simplicity，sensitivity and high accuracy，the method could be applied in the determination of aflatoxin B1 in vegetable oil.