In order to investigate the mechanism of magnetic memory effect in the process of friction,magnetic domains in the rubbing contacting area were in situ observed by Bitter powder pattern.The surface magnetic field of wear scar under the different sliding cycles and different friction load was measured,and the changes of magnetic domain in the rubbing contacting area were observed over time.Experiments show the surface magnetic field of wear scar experiences a threestage process:intense variation,slow increase,steady stage.The domain wall in the friction contact area turns perpendicular to the direction of reciprocating friction during the friction process,the thickness and spacing of the domain wall is increased,and the shape of the domain wall presents a curved shape,and these changes of the domain wall are more obvious when the friction load is 40 N than when it is 20 N.After the friction,the magnetic domain structure experiences aging changes,and the state of domain wall within the contact area begin to dissipate after 60 days under the earths magnetic field,and the dissipation degree is smaller when the friction load is 40 N than when it is 20 N.