Air　circuit　breaker　(ACB)　is　widely　used　in　power　distribution　system.　The　movable　contact　of　ACB　consist　of　multiple　parallel　contacts　and　the　arc　will　be　ignited　when　the　short-circuit　current　appears.　This　paper　focuses　on　the　arc　motion　process　in　multiple　parallel　contacts　system.　A　3-D　magneto-hydro-dynamic　(MHD)　model　of　multiple　parallel　contacts　system　is　built.　In　this　model,　the　nonlinear　B-H　curve　of　splitter　plate　is　used　in　calculation.　The　magnetic　vector　potential　approach　is　adopted　to　calculate　the　time-varying　electromagnetic　field　produced　by　the　current　loop.　The　difference　of　voltage　drop　between　near-anode　and　near-cathode　is　considered.　In　addition,　the　interaction　among　multiple　parallel　contacts　is　included　in　numerical　simulation.　Based　on　this　calculation,　the　arc　voltage,　temperature　and　current　density　were　obtained.　The　arc　motion　process　is　analyzed　by　current　density　and　temperature.　The　simulation　results　show　that　the　anode　arc　root　will　appears　on　multiple　contacts　with　the　increase　of　current.　The　upper　arc　moves　faster　than　low　arc　after　the　arc　column　is　divided　by　the　splitter　plate.