Gold-silver (Au-Ag) alloy nanostructures were fabricated on substrate by the highly intense femtosecond laser pulses through a wet photochemical reduction without introducing additional reducing agent. The nanostructures can not only retain the characteristic of metallic materials, but also realize the assembling pattern of arbitrary subtle shape. The formation of Au-Ag alloy nanostructures was confirmed by energy dispersive X-ray (EDX) diffraction, indicating the fabricated nanostructures were different in the ratio of gold to silver for different molar ratios in the solution. The composite metal material was applied for catalysis of hydrogen peroxide and an ideal result was achieved.