Abstract: A unified model is establtshed for the liquid zone, mushy zone and solid zone during laser-plasma hybrid welding, which takes into account the surface tension, heat buoyancy and electromagnetic force in the welding pool. The velocity and temperature distributions in weld pool were numerically computed to study the effect of electromagnetic force on the flow and convection heat transfer in weld pool. Results show that the electromagnetic force's effect is negligible and the surface tension is predominant at the initial formation phase of weld pool. With the increasing of the depth of weld pool, the eddy induced by electromagnetic force appears at the bottom of weld pool and results in deeper and wider weld pool. The hybrid welding experiments on 1420 Al-Li alloy show that the computational results agree well with experimental results.