Keyhole-induced　pores　(KIPs)　are　common　defects　in　products　of　laser-arc　hybrid　manufacturing,　seriously　deteriorating　their　fatigue　resistance.　In　this　study,　the　effects　of　the　hybrid　heat　source　on　the　formation　of　KIPs　are　investigated.　Many　KIPs　appear　in　the　molten　pool　if　the　laser　and　arc　energies　of　the　laser-TIG　hybrid　heat　source　are　roughly　the　same,　while　a　few　KIPs　are　observed　when　either　laser　or　arc　energy　dominates.　The　laser　-arc　energy　ratio　had　almost　no　impact　on　the　formation　of　KIPs　when　the　TIG-laser　hybrid　heat　source　was　used;　however,　the　porosity　increased　and　then　dropped　with　the　arc　current.　The　performed　numerical　calculations　and　analysis　show　that　the　arc　can　drive　the　molten　liquid　near　the　keyhole　mouth　to　block　the　keyhole　to　form　bubbles　and　interrupt　the　bubble　escape　from　the　molten　pool.　This　is　the　main　cause　of　the　keyhole　instability　and　collapse,　as　well　as　the　consequent　formation　of　KIPs.