The Er-doped AlN films were deposited on (0001) sapphire substrates by radio frequency reactive magnetron sputtering. The Xray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and impedance analyzer were used to characterize the crystal structure and electrical properties of films prepared at different substrate temperature. The results indicated that the crystal orientation and surface roughness were getting better and better with the increase of substrate temperature, while the crystal orientation and surface roughness began to deteriorate when the temperature continued to rise, the properties of the resistivity and leakage current were getting better at the start with the increase of temperature and then the performance began to decline. The film structure and electrical properties are best when the substrate temperature is 200 ℃.