A new technology using flux pieces constraint arc plug welding to manufacture high strength steel sandwich board is proposed to solve the lack of fusion of T joint between core board and panel in the laser welding of sandwich board. The arc combustion from and the changing process of molten pool are studied by using high speed photography, and the mechanical property of T joint is tested. The results show that the flux pieces can compress and stabilize the arc,enhance the welding thermal efficiency and promote the metal transfer.When using φ1.6 mm welding wire,the groove root gap is 5,6, mm and appearance of weld is well. When welding current is constant,as the arc voltage increases,the change law of joint successively presents "incomplete penetration", "well appearance", "arc’s another climbing incomplete penetration" and "welding leakage". Constraint arc plug welding range:arc voltage 20 ,2,4,V,welding current160,3,00 A,welding speed 5 mm/s.