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Magnetic reconnection in the Earths magnetotail accelerates fast plasma jets.The front edge of the earthward propagating jet is a type of discontinuity,called the dipolarization front (DF).The DF is characterized by an abrupt increase in the ZGSM-component of the magnetic field mainly.The spatial scale and occurrence rate of dipolarization fronts (DFs) are investigated by using all four Cluster magnetic field data from 2001 to 2009 in this study.Altogether 674 DFs have been observed by the Cluster satellites,but far from all of them by all spacecraft simultaneously.For example,only 202 DFs are observed by Cluster 1 (C1).Therefore the single satellite observations cannot tell the true distribution of DFs.