Previous researches have extensively explored the use of concrete as an infill material for hollow steel sections, but there is limited reference on other types of infill materials.This study investigates the use of various infills, including wood, glulam, and H-beam, in square hollow steel braces to enhance buckling strength, widen stress concentration in the mid-span, and broaden the accumulation of plastic strain to delay local buckling and prolong the fracture cycle life of the brace. The proposed finite element method was utilized to assess the cyclic behavior of the braces, validated through three types of experimental tests on both unreinforced specimens and brace with infill material. An analysis was then conducted on 21 models to examine important parameters, such as section width-to-thickness ratio, flexural rigidity, filler length, and filler material. The results show that infill materials extend the von-Mises stress distribution at mid-span and reduce the PEEQ ratio. Additionally, the infill strengthens the buckling resistance of the brace; however, the effect of the infill does not significantly increase in models with lower width-to-thickness ratios. The infill also helps to improve the ductility ratio and energy dissipation capacity of the brace. From the fracture point of the hysteresis loop, the specimens with infill wood or glulam, as well as the specimens with shortened infill length, all demonstrate an ability to prolong the cycle life of the braces. Moreover, specimens with larger flexural rigidity of infill H-beam dramatically improve the fracture cycle life, which is also favorable for extending the life of the brace before rupture. However, it is recommended that the flexural stiffness ratio should be kept below a certain threshold to prevent buckling mechanisms in the transition zone.