High-strength quenched and tempered (HSQT) steels have been widely used in structural applications where light weight is of primary design interest.Gas metal arc welding is a common way to join QT steels.When GMAW is used to join the HSQT steel,multi-pass is usually required to achieve full penetration.In addition,weld crack is often observed because of HSQT steel’s high susceptibility to hydrogen embrittlement.In addition,due to the large amount of heat input from the arc,the heat affected zone is often softened.This reduces the ductility and strength of welds and makes the weld weaker than the base metal.In this study,a hybrid laser/GMAW process is proposed to produce butt joint for 6.5mm thick HSQT A514 steel plate.Hydrogen diffusion mechanism is first discusses for GMAW and hybrid laser-GMAW welding processes.Metal transfer mode during the hybrid laser/GMAW welding process is also analyzed.A high speed CCD camera with 4000 frame/second is used to monitor the welding process in real time.Welds obtained by GMAW and hybrid laser/GMAW techniques are compared and tested by static lap shear and dynamic impact.Effects of gap between two metal plates and laser beam/GMAW torch spacing on weld property are studied.By appropriately choosing these two parameters,crack-free butt joints with full penetration can be successfully obtained by the hybrid laser/GMAW welding process for HSQT A514 steel plate. High-strength quenched and tempered (HSQT) steels have been widely used in structural applications where light weight is of primary design interest. Gas metal arc welding is a common way to join QT steels. When GMAW is used to join the HSQT steel, multi -pass is usually required to achieve full penetration. In addition, weld crack is often observed because of HSQT steel’s high susceptibility to hydrogen embrittlement. In addition, due to the large amount of heat input from the arc, the heat affected zone is often softened .This reduces the ductility and strength of welds and makes the weld weaker than the base metal. In this study, a hybrid laser / GMAW process is proposed to produce butt joint for 6.5mm thick HSQT A514 steel plate. Hydrogen diffusion mechanism is first for GMAW and hybrid laser-GMAW welding processes. Metal transfer mode during the hybrid laser / GMAW welding process is also also analyzed. A high speed CCD camera with 4000 frame / second is used to monitor the welding process in real Welds obtained by GMAW and hybrid laser / GMAW techniques are compared and tested by static lap shear and dynamic impact. Effects of gap between two metal plates and laser beam / GMAW torch spacing on weld property are studied. Commercially these two parameters , crack-free butt joints with full penetration can be successfully obtained by the hybrid laser / GMAW welding process for HSQT A514 steel plate.