Abstract: DW10,15 series automatic air switch was applied with the low-voltage fuse in low-voltage distribution system.When short circuit occurred in one feedback branch,leapfrog trip would happen in the system and the power cut field would spread.Because there was a cooperation problem between the action time of the transformer switch secondly and the melting time of the fuse.This paper analyzed the reason of the leapfrog trip,and presented the improved method which was carried into execution and reach good effect.The relevant steps were introduced in detail which provided reference for the improving of the low-voltage distribution equipment performance.