Abstract: In a mega frame structural system, its outrigger trusses connect its surrounding mega tubes to increase the resistance to bending moments and significantly enhance its overall stiffness. This study investigates the mechanical performance of bidirectional joints between outrigger trusses and seismic-resistant walls through a case study of a mega structure. The specimens are primarily categorized into bidirectional joints of outrigger trusses with double-steel-plate shear walls and outrigger trusses with reinforced concrete (RC) shear walls. Quasi-static tests were conducted on both specimens to comparatively analyze the failure mechanisms, seismic performance, and force transfer mechanisms of the joints. The experimental results indicate that both types of joints exhibit an excellent aseismic performance, and that the outrigger trusses can effectively connect adjacent components while reliably transferring forces. The compressive buckling deformation and weld fractures occurred in the upper and lower chords of the outrigger trusses; the joint region of the outrigger truss–double-steel-plate shear wall specimen remained elastic, while the outrigger truss–RC shear wall bidirectional joint demonstrated higher stable bearing capacity, though significant damage was observed in the RC shear wall. The findings of this study can provide a reference for the application of outrigger truss–aseismic wall joints in mega structures.