In order to reveal the reason why mechanical properties of alloy films increase continuously after amorphizing, a series of Al-Zr alloy films with different Zr contents are prepared by magnetron co-sputtering of Al and Zr targets. The microstructure and mechanical properties of the films are characterized through a number of techniques, including X-ray energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and nanoindentation. Results show that the films with low Zr content form highly supersaturated solid solutions due to high dispersibility of vapor particles and non-equilibrium growth of the film in co-sputtering process. The film grains are refined to nanoscale particles due to dramatic lattice distortion and the film hardness increases rapidly. As Zr content increases, the film hardness increases continuously because of the increase of Al-Zr chemical bonds after amorphizing, and reaches a high value of 9.8 GPa at 33.3 at.% Zr. The research results reveal the effect of the Al-Zr chemical bonds on mechanical properties in amorphous films