This paper presents a novel composite energy-dissipation beam-column joint that incorporates friction side plates (FSPs) and composite energy-dissipation boxes (EDBs). As replaceable components of this innovative joint, the composite EDBs significantly influence its overall seismic performance. To conduct a comprehensive study of the composite EDBs, eight specimens were fabricated, with parameters including filling material, construction gaps, and secondary loading. This investigation primarily examined the failure modes, hysteretic performance, strength degradation, stiffness degradation, and energy-dissipation capacity of the composite EDBs. The results indicated that increasing the construction gap can delay the buckling of dog-bone energy-dissipation plates (DB-EDPs), while secondary loading enhanced both the strength and stiffness of the specimens. Additionally, the filling material effectively restrained the out-of-plane buckling of the DB-EDPs, thereby improving the load-bearing capacity of the composite EDBs. The effectiveness of the filling materials was ranked as follows: wood > steel box > rubber. Finally, a theoretical load-bearing capacity formula for the specimens was derived, and the applicability was validated by comparing the experimental values with the theoretical predictions.