Vacuum　circuit　breakers　(VCBs)　are　widely　used　in　power　distribution　systems.　When　the　VCB　in　a　switchgear　interrupts　the　short　circuit　current,　the　U　type　loop,　which　consists　of　a　vacuum　interrupter,　an　external　busbar　and　a　conductive　rod,　generates　an　external　transverse　magnetic　field　(ETMF).　This　field　deflects　the　vacuum　arc　and　affects　the　interruption　performance　of　the　VCB.　In　this　paper,　the　real　magnetic　field　data　of　the　arc　region　are　obtained　by　establishing　a　simulation　model　of　an　electrode　system,　taking　into　account　the　real　ETMF　and　real　axial　magnetic　field　(AMF).　Furthermore,　the　three　dimensional　steady　magnetohydrodynamic　model　of　the　vacuum　arc　is　established　by　using　real　magnetic　field　data　as　the　boundary　condition.　The　vacuum　arc　characteristics　under　the　combined　effect　of　AMF　and　the　asymmetric　transverse　magnetic　field　(TMF)　are　studied.　The　simulation　results　show　that　the　ETMF　considerably　changes　the　Bx　of　the　arc　column,　which　demonstrates　asymmetry　in　the　positive　and　negative　directions,　whereas　By　demonstrates　a　weaker　asymmetry.　Moreover,　the　asymmetric　TMF　deflects　the　distributions　of　the　vacuum　arc　plasma　and　increases　the　partial　heat　flux　density　and　axial　current　density.　With　the　increase　in　the　severity　of　the　short　circuit,　the　TMF　asymmetry　of　the　arc　region　is　enhanced　and　the　deflection　of　the　vacuum　arc　plasma　is　also　enhanced.　©　2020　Author(s).