The power density of TaN thin film resistors which are prepared on Ni-Zn ferrite substrate by DC magnetron sputtering could just reach 0.91 W/mm2 owing to the bad surface and internal structure feature as well as the low thermal conductivity of the ferrite substrate. The AlN thin film buffer layer with thickness of 1.5 μm was plated between ferrite substrate and thin film resistors by RF magnetron sputtering. The surface feature and the heat dissipation of the substrate can be improved effectively.The power density of TaN thin film resistors with the AlN thin film buffer layer can be up to 3.76 W/mm2.