Since the copper could not be nitrided, the conventional surface hardening method can not be used to improve the surface hardness of the copper. In this paper, the stability and hardness of N-containing Cu alloy films were studied by adding Ti which could stabilize N to Cu alloy films, and the effective method of improving the surface hardness of the copper was further explored. The Cu alloy films containing different content of Ti, N were deposited onto the Si (100) substrates by magnetron sputtering and their microstructure, hardness and resistivities were analyzed. The result suggests that the addition of Ti could make N exist in Cu alloys films in the form of Ti-N compounds, and the hardness of the alloy films was improved compared with that of pure Cu film (~3.5 GPa). Especially, the hardness of Cu80.2Ti9.8N10.0 film was still up to 5.4 GPa even after annealing at 400 ℃ for 1 h. The resistivity of the Cu81.2Ti9.9N8.9 film (~660 μΩ?cm) with large contents of Ti and N was much higher than that of Cu88.5Ti4.3N7.2 film (~123 μΩ?cm), but the two films were about the same hardness (~5.2 GPa). Therefore, the Ti, N contents should be controlled properly when preparing Cu(Ti, N) films.