Rolled AA7020-T651 with 2 mm thickness are welded by a hybrid laser arc heat source system with the ER5356 filler. The microstructure and mechanical performance of hybrid welded joint are investigated by optical microscope, scanning electron microscope, Shanghai synchrotron radiation X-ray micro-tomography, electron backscattered diffraction, micro-hardness, tensile properties and finite element simulation. The results show that the weld zone, fusion line and base mental exhibit cast equiaxial dendrites, large columnar crystal and stretching rolling structure, respectively. Moreover, a fine grain zone with about 100 μm in width near the heat affected zone is observed clearly. The tensile strength, yield strength, elongation and welding coefficient are 260 MPa, 213 MPa, 4.8% and 0.7, respectively. Central hybrid weld has the lowest hardness (75 HV), which is about 62.5% of base metal, presenting a serious strength loss. This is mainly due to serious evaporation losses and redistribution of strengthening element Zn as well as the precipitate particles modifications during the hybrid welding process. Finite element analysis suggests that the undercut similar to a notch near weld toe rather than central weld zone with the lowest hardness is the fundamental reason to the fatigue failure of in-service hybrid welded joints.