The influence of medium-frequency sputtering process on the structure of Ni-AlN composite films and graded Ni-AlN selective absorbers was studied. Results show that the critical nitrogen flow rates are decreased corresponding to the change of aluminum sputtering mode from metallic mode to reactive mode with increasing nickel target current and decreasing aluminum target current; the nickel content in Ni-AlN composite films is increased with the rise of nickel target current, while the variety of the aluminum content and N/Al atomic ratio with nickel target current is inverse; metallic aluminum phase is apt to be formed in the Ni-AlN composite films deposited at higher nickel target current. When the deposition duration for a Ni-AlN composite layer is increased, the composition distribution of Ni-AlN selective absorbers in depth is shifted from the gradual changing to the stepped changing, and the visible light reflectivity is decreased. A visible light reflectivity of about 10% and a good spectral selectivity is obtained when the deposition duration for a Ni-AlN composite layer is 10 min