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we use the magnetic field data from C/NOFS after correcting the interpolation data to study the MLT variations and the propagations of magnetic perturbations, and their relationships with interplanetary parameters.By fitting the measurements during 32 magnetic storms in 2008-2013 with off-center ellipses, we find the MLT variations of magnetic perturbations produced by the ring current are widely dawn-dusk asymmetric and partly day-night asymmetric in main phase which can indirectly reflects the asymmetry of the ring current.Besides, the asymmetry changes from dawn-dusk to day-night.So we consider a dusk-centered partial ring current often shifts eastward to the night side in about 10 hours, and then reduces during the recovery phases of some storms.We think it is because of the continuous enhancing of dawn-dusk convection electric field and the shielding electric field caused by dawn-dusk convection electric field.Finally, we discuss the relationships between the variations of northward magnetic perturbations and the interplanetary parameters, and find significant variations of all solar wind parameters can affect the intensity of ring current.IMF Bz has a great influence on the intensity of northward magnetic perturbations and the dawn-dusk asymmetry of northward magnetic perturbations.It is because IMF Bz can drive convection electric field which has a great influence on the intensity and the dawn-dusk asymmetry of ring current.