(Fe₇₃Ga_27-xAl_x)_99.8Tb_0.2 (x=0, 1, 2, 3, 4, 5) alloys were prepared by vacuum arc furnace to investigate the effect of Al addition on the microstructure, magnetic properties, and mechanical properties of alloys. Results show that the phase structure of the alloys is still A2 phase and Tb₂Fe₁₇ phase, and the metallographic structure is composed of cellular crystal and columnar dendrite. The decrease in lattice constant, the intensification of (100) orientation, and the generation of Tb₂Fe₁₇ phase at the grain boundary exert significant effect on the magnetostrictive properties. The fracture morphology of the alloys is intergranular brittle fracture and cleavage fracture, and the causes of fracture occurrence include the segregation of Tb and Al elements. The parallel magnetostrictive strain (λ_∥) of (Fe₇₃Ga₂₄Al₃)_99.8Tb_0.2 alloy peaks at 1.04×10^-4. It is worth noting that compared with those of (Fe₇₃Ga₂₇)_99.8Tb_0.2 alloy, the λ_∥ and elongation of (Fe₇₃Ga₂₆Al₁)_99.8Tb_0.2 alloy increase by 18.3% and 53.4%, respectively. Besides, (Fe₇₃Ga₂₆Al₁)_99.8Tb_0.2 alloy possesses the characteristics of high saturation magnetization (M_s), low remanent magnetization (M_r), and coercivity (H_c), which is beneficial to reduce the cost in actual production, but its tensile strength and Vickers hardness decrease to a certain extent. Therefore, the investigation on the micro-mechanism of Al addition on Fe-Ga alloys is of great significance for the development of Fe-Ga alloy devices.