The influence of Ga doping on the structure and mechanical properties of B2-CuZr phase reinforced larger-size CuZrAlY metallic glass composites was investigated by experiments and simulations. The result showed that as Ga content increased, the glass-forming ability of CuZrAlY metallic glass composites was gradually enhanced. Section morphology and thermal analysis indicated that Ga doping induced the decreased content of the crystals and the enlargement of the super-cooled liquid region, and increased activation energy for crystallization. Ga also stabilized the B2-CuZr phase. Characterization of the microstructure and mechanical test results suggested that the B19''''-CuZr phase disappeared in the as-cast samples after adding Ga, and the martensitic transformation of the B2-CuZr phase was hindered when Ga content increased. The evolution mechanism of mechanical behaviors of the CuZr-based metallic glass composites during Ga doping was clarified by first-principles calculation. The results would be beneficial to the development and application of large-size CuZr-based metallic glass composites.