In recent years high temperature superconducting materials and the refrigerating machine technology have advanced so extensively, that the helium free superconducting magnet can provide strong magnetic fields of about 10 T easily. Magnetic substances in a strong magnetic field is expected to produce a high gradient magnetic field near their surfaces. A study has been made on the magnetic field effect on the behavior of oxygen and water near a steel surface submerged in water in strong magnetic field. We have found differences in corrosion of the steel surface along the gradient magnetic field, and the shape change of water surface has been observed. Further, the relation between the corrosion pattern and magnetic field gradient has been made clear from the analysis of the magnetic field distribution around the steel.