Abstract: After?the?grounding?of?the?first?DC?system?occurs?in?a?220kV?substation,?the?220kV?first?set?of?bus?protection?and?the?110kV?first?bus?protection?send?out?"switch?shift?and?bus?interconnection?signals,?affecting?the?normal?operation?of?bus?protection".?In?this?paper,?the?fault?phenomenon?is?combined?to?carry?out?the?cause?analysis?of?the?bus?protection?missent?Internet?alarm.