During　the　interruption,　the　separation　of　the　contacts　plays　an　important　role　in　different　kinds　of　switch　gears　since　the　arc　motion　or　the　arc　elongation　will　be　affected.　The　movement　of　the　contact　could　increase　the　arc　length　and　then　decide　the　arc　behavior.　In　reverse,　the　arc　current　will　be　changed　during　the　interruption　and　the　Lorentz　force　will　then　influence　the　movement　of　the　contact.　It　is　necessary　to　consider　this　phenomenon　to　make　the　arc　simulation　more　accurate　and　universal.　In　this　work,　low　voltage　arc　plasma　simulation　in　3D　with　contact　opening　process　has　been　established.　Both　the　sheath　and　nonlinear　magnetic　material　were　taken　into　consideration.　Calculation　was　based　on　magneto-hydrodynamic　arc　model,　and　a　method　of　coupling　different　software　to　separately　calculate　fluid　and　electromagnetic　field　has　been　developed　to　fulfill　the　requirements　above.　Furthermore,　a　low　voltage　circuit　breaker　has　been　tested　to　validate　the　simulation　with　U-I　characteristics.　©　2019　IEEE.