Due　to　the　compact　structure　of　the　HVDC　relay　contact　system,　it　is　difficult　to　use　grids　or　gas　producing　materials　to　improve　the　breaking　performance　of　the　contacts.　The　arc　movement　speed　can　be　accelerated　by　the　external　magnetic　field　of　the　magnetic　blowing　system,　which　improves　the　arc　extinguishing　ability.　As　a　key　part　of　the　magnetic　blowing　system,　the　permanent　magnet　has　an　uneven　distribution　of　external　magnetic　induction,　and　its　size　has　a　great　influence　on　the　size　and　distribution　of　the　magnetic　field,　which　causes　certain　difficulties　for　the　design　of　the　magnetic　blowing　system.　In　response　to　this　problem,　this　paper　established　a　3D　finite　element　model　of　the　magnetic　blowing　system,　focusing　on　the　analysis　of　the　impact　of　the　permanent　magnet　size　on　its　external　magnetic　field,　and　established　a　relevant　mathematical　model.　It　also　analyzed　the　characteristics　of　the　external　magnetic　field　distribution　of　the　permanent　magnet,　and　obtained　the　relationship　between　the　uniformity　of　the　external　magnetic　field　distribution　and　the　size　of　the　permanent　magnet.　Finally,　combined　with　the　characteristics　of　the　HVDC　relay＇s　breaking　arc,　this　paper　designed　the　size,　magnetization　direction　and　installation　position　of　the　permanent　magnet　in　the　magnetic　blowing　system　by　considering　the　force　and　stagnation　time　of　the　arc.　It　lays　a　theoretical　foundation　for　improving　the　contact　breaking　performance　of　HVDC　relays.　©　2022,　Electrical　Technology　Press　Co.　Ltd.　All　right　reserved.