A　welding　arc　is　considered　a　composite　of　electron　flow　and　electrically　neutral　arc　plasma.　Their　interaction　significantly　affects　the　transmission　and　conversion　process　of　the　heat　and　momentum　in　welding　process.　Studying　the　electrical　property　of　arc　plasma　is　significant　for　understanding　this　interaction,　but　directly　testing　such　property　in　arc　column　is　still　a　challenge.　In　this　paper,　a　novel　method　based　on　active　probes　was　proposed/designed　and　used　to　test　such　a　property　in　a　welding　arc　plasma.　The　probes　were　partially　coated　to　electrically　insulate　except　for　their　tips.　During　test,　the　probes　moved　into　the　arc　zone　to　detect　the　resistance　between　the　tips.　To　minimize　the　damage　to　the　probes,　the　movement　of　the　probes　was　relatively　quick　such　that　the　stay　of　the　tips　in　the　arc　zone　is　minimal.　In　the　meantime,　electrical　signals　of　the　detection　circuit　and　arc　images　were　collected　by　a　data　acquisition　system　and　a　high-speed　camera　system.　Images　suggested　that　the　movement　of　the　probes　imposed　no　noticeable　effect　on　the　behavior　of　the　arc.　On　the　other　hand,　the　voltage　to　current　ratio　(V-I　ratio)　between　the　probe　tips　reduces　as　the　moving　speed　of　the　tips　reduces.　Analysis　suggests　that　the　detection　circuit　is　not　purely　resistive.　As　such,　when　the　moving　speed　was　reduced　sufficiently,　the　ratio　approaches　to　a　constant　without　changing　with　the　moving　speed.　The　effect　from　the　dynamic　property　of　the　circuit　on　the　measurement　of　the　V-I　ratio　was　thus　eliminated.　As　such,　the　moving　speed　can　be　selected　such　that　the　dynamic　behavior　of　the　detection　circuit　becomes　insignificant　while　the　speed　is　still　sufficient　to　minimize　possible　damage　to　the　tips　due　to　high　temperature　of　the　arc.　Furthermore,　the　parameters　of　detection　circuit　were　also　discussed.　As　such,　a　novel　method　becomes　available　to　study　the　electrical　behavior　of　the　arc　plasma　in　the　future　study.　(C)　2017　The　Society　of　Manufacturing　Engineers.　Published　by　Elsevier　Ltd.　All　rights　reserved.