Wire　arc　additive　manufacturing　(WAAM),　utilizing　welding　arc　to　melt　metal　wire　into　shaped　parts,　has　become　a　promising　manufacturing　technology　recently.　Tandem　GMAW-based　WAAM　(TG-WAAM),　in　which　two　wires　are　fed　into　the　molten　pool　simultaneously,　has　the　potential　to　double　the　efficiency　of　traditional　WAAM.　However,　the　high　wire-feed　speed　is　accompanied　with　high　heat　input　that　is　likely　to　cause　molten　pool　overflowing,　especially　at　upper　layers　because　of　decreased　heat　dissipation　and　increased　heat　accumulation.　An　in-process　active　cooling　technology　based　on　thermoelectric　cooling　is　introduced　into　TG-WAAM　in　this　research.　Its　effect　on　forming　quality　and　efficiency　of　TG-WAAM　is　investigated　experimentally.　The　results　show　that　the　additional　cooling　well　compensates　for　the　excessive　heat　input　into　the　molten　pool,　which　enables　not　only　increased　maximum　wire-feed　speed　(9-15%)　but　also　reduced　inter-layer　dwell　time　(42-54%),　while　maintaining　the　desired　forming　quality.　The　overall　efficiency　is　improved　by　more　than　0.97　times　in　the　case　study.　This　research　provides　a　feasible　scheme　to　solve　the　conflict　between　forming　quality　and　efficiency　during　WAAM.