In order to improve the anti pressure capability of magnetic fluid seal under the large gap condition, a novel diverging stepped magnetic fluid seal was designed and set the pole teeth on the stepped shaft. The magnetic field distribution in the gap of diverging stepped magnetic fluid seal were numerical simulations by the finite element method of magnetic field. The effects of axial pole teeth number, radial pole number, radial sealing gap height and axial sealing gap on the anti pressure capability of a novel diverging stepped magnetic fluid seal were studied. The results show that the anti pressure capabilities of magnetic fluid seal increase with the increase of axial pole teeth numbers. The anti pressure capabilities of magnetic fluid seal firstly decrease and then increase with the increase of radial pole teeth numbers. The anti pressure capability of magnetic fluid seal firstly decreases and then increase with the increase of radial sealing gap height. The anti pressure capabilities of magnetic fluid seal decrease with the increase of axial sealing gap width.