Zn0.95-xCo0.05CuxO (x=0-8%) thin films were fabricated on Si (111) substrate by reactive magnetron sputtering method.Detailed characterizations indicate that the doped Cu ions substituted the Zn2+ ions in ZnO lattice.The doped Cu ions are in +1 and +2 mixture valent state.The ferromagnetism of the Zn0.95-xCo0.05CuxO film increases gradually with the increasing of the Cu+ ions concentration till x=6%, but decreases for higher Cu concentration.Experimental results indicate the increase of ferromagnetism is not owing to the magnetic contribution of Cu+ ions themselves, but owing to the enhancement of magnetic interaction between Co2+ ions, which suggests that p-type doping of Cu+ ions play an important role in mediating the ferromagnetic coupling between Co ions.