The physical process in the Earths polar region is very complex and still needs to be further studied.Using the data from Cluster satellite measurement,an analysis on field-aligned electrons in the mid-latitude cusp on 30 September 2001 has been performed.The satellite observed a down-flowing electron event in the low-latitude boundary and a sequential up-flowing electron event in the high-latitude boundary of the cusp region.The downflowing electron had a velocity as high as 500km/s and a flux of 2.0 × 109 cm-2.s-1.The up-flowing electron had a velocity up to 1200km/s and a flux of 4.9 × 109 cm-2·s-1.Both the velocity and the flux observed in this event are the maximum values of the up-flowing electrons observed by all satellites to date.The electron is the main contributor for the field-aligned current in this event.The physical mechanism is also discussed.The down-flowing electron in the low-latitude boundary of the cusp region may result from solar wind injecting during the southward IMF,and the up-flowing electrons in the high-latitude boundary of cusp may result from mirroring of the solar wind,or from the ionospheric up-flowing electrons which have been accelerated.