Directed　Energy　Deposition-Arc　(DED-Arc)　are　dedicated　to　large　parts　manufacturing.　To　satisfy　the　thermal　force　and　mass　requirements　while　utilizing　the　physical　characteristics　of　the　arc　electrode,　a　mechanism　and　technology　for　alternating-arc-based　additive　manufacturing　is　proposed　through　a　polarity-switching　self　-adaptive　shunt　(PSSAS).　Experimental　results　show　that　on　the　two　parallel　branches,　the　current　can　only　alternately　flow　through　the　welding　wire　or　the　substrate.　The　arc　burns　alternately　between　the　combination　of　＂welding　wire　-tungsten　electrode＂　and　＂tungsten　electrode　-substrate＂,　forming　an　electronegative　arc　with　the　wire　as　the　anode　and　an　electropositive　arc　with　the　substrate　as　the　cathode.　The　decoupling　control　of　thermal　force　and　mass　transfer　can　be　achieved　by　EN　arc　(tungsten　electrode　negative,　wire　positive)　to　control　the　melting　of　the　wires　and　size　and　temperature　of　droplets,　EP　arc　(tungsten　electrode　positive,　substrate　negative)　to　control　the　cathode　cleaning　and　molten　pool　temperature.　When　the　deposition　velocity　is　5.7　mm/s　and　the　wire　height　is　8　mm,　the　molten　drops　exhibit　a　frequency　of　one　pulse　per　drop,　which　will　produce　well　weld　quality　with　minimal　defects　and　spatter.　The　dilution　of　the　deposited　layer　reaches　0.05　and　the　width-to-depth　ratio　is　17.47　with　these　parameters.　The　proposed　method　reduces　the　heat　input　to　the　base　metal　and　improves　the　heat　input　to　the　wire　compared　with　conventional　processes,　resulting　in　better　melting　efficiency.　Thus,　PSSAS　provides　a　new　theory　for　high-precision　and　high-efficiency　additive　manufacturing.