In　order　to　establish　the　relationship　between　the　external　and　internal　characteristics　of　contact　arc,　taking　the　magnetic　latching　relay　as　research　object,　this　paper　conducts　arc　image　collection　and　morphological　treatment　of　the　breaking　arc.　With　the　parameters　variation　law　of　arc　image　area　studied　quantitatively,　the　changes　of　arc　area　with　time　and　current　are　analyzed.　With　the　arc　images　captured,　the　arc　voltage　and　arc　current　waveforms　are　acquired　simultaneously.　By　the　numerical　analysis　to　curve　fitting　the　data,　the　correlation　between　arc　area　and　arc　power　of　the　breaking　process　is　achieved.　The　results　show　that　under　the　different　currents,　the　variation　trend　of　the　arc　image　area　is　almost　the　same.　The　maximum　pixel　area　of　the　arc　increases　with　the　load　current.　When　the　breaking　current　is　relatively　higher,　the　change　of　morphological　arc　images　is　divided　into　two　stages,　that　is,　arc　area　fast　increase　stage　and　slow　decrease　one,　and　there　are　the　fifth　power　and　biquadrate　relation　between　the　arc　area　and　arc　power,　respectively.　This　study　provides　a　new　idea　for　predicting　the　arc　magnitude,　the　combustion　degree　and　the　extinction　difficulty　degree　by　the　external　characteristics　of　electrical　apparatus.　©,　2015,　Chinese　Machine　Press.　All　right　reserved.