Abstract: Dust tended to buildup in the chamber of the electromagnet for foil rejecting in ZB45 packer, which resulted in askew foil feeding.By connecting an air pipe to the chamber to keep it in a positive pressure state, the dust buildup was avoided.This improvement has been introduced into 26 ZB45 packers, no dust was found in the chamber of electromagnet, and the askew foil feeding caused by dust buildup in electromagnet reduced from 20 times per month to 0.