In-situ tensile test of 2219 aluminum alloy joint by electric current supported laser welding laser under electric current is carried out using scanning electron microscope. In-situ tensile test is employed to study the crack formation, propagation and fracture mode of welded joint, and the micro fracture behavior is studied.The relationships between microstructures and mechanical properties are revealed.The results show that the crack initiation mainly arises on the interface between eutectic phase and matrix and in the matrix between dendrites in the weld zone.The crack propagation is done in two ways of intergranular and transgranular propagation,and the crack propagation is prevented obviously by eutectic phase. The samples break with the mixed model of normal fracture and shear fracture in the weld zone.The effects of electric current on refining solidfication structure, homogenizing eutectic phase and increasing solute solid solution in the weld matrix prevent the crack formation and propagation,which is help the to increase the strength of aluminum alloy welded joint.