Abstract: Objective To understand influence of aging system on fracture behavior of welded structural parts of Al-0.55Mg-0.76Si aluminum alloy extruded profiles, this paper provided a theoretical basis for improving fracture behavior of welded structural parts. Methods The welded structural parts of Al-0.55Mg-0.76Si aluminum alloy extrusion profiles were taken as the research object, and fracture behavior was analyzed by metallographic structure, SEM, EDS, tensile and bending methods at room temperature. Results The results showed that after the two-stage aging treatment, the second phase increased significantly. With the extension of aging time, the second phase appeared coarsening. The second phase was Mg and Si phase according to micro-surface composition analysis. The strength and elongation of Al-0.55Mg-0.76Si aluminum alloy welded structural parts under two-stage aging system were higher than those under single-stage aging, and fracture morphology changed from plastic-brittle fracture to plastic fracture. Bending angle of Al-0.55Mg-0.76Si aluminum alloy welded structural parts under two-stage aging system was higher than that under single-stage aging, and crack gradually changed from intergranular fracture to transgranular fracture. When aging system was 150 ℃×1 h+180 ℃×5 h, the strength was the highest, yield strength was 191.2 MPa, and tensile strength was 218.4 MPa. The plasticity was better, fracture morphology was plastic fracture, length of crack on the outer surface of bending samples became shorter, which was 109 μm, and crack on the inner surface was transgranular fracture. Conclusion Comprehensive analysis showed that when aging system was 150 ℃×1 h+180 ℃×5 h, the strength and plasticity of Al-0.55Mg-0.76Si aluminum alloy extruded structural parts were the best, which was the best process system.