A series of aluminum matrix nanocomposite films are synthesized by magnetron sputtering of Al and TiN targets. The composition, microstructure and mechanical property of the composite film are characterized by energy dispersive spectroscopic, X-ray diffraction, transmission electron microscope and nanoindenter. The influences of (Ti, N) content of supersaturated solute Ti,N atoms on the microstructure and mechanical property of the composite films are investigated. The results reveal that the composite film with adding Ti,N atoms together forms a dual-supersaturated solid solution exhibiting both features of substitutional and interstitial solid solution. Higher solute content induced gradual evolutions of nanocrystallization and amorphization of grains in film and solute enrichment occured at the grain boundaries. Correspondingly, the composite film containing 1.8 at.% (Ti, N) can rapidly reach a hardness of 3.9 GPa, and further increasing TiN content to 17.1 at% (Ti, N) the film hardness achieves 8.8 GPa demonstrating the significant strengthening effect of dual-supersaturation of Ti and N on aluminum film.