In this study, the ErAlN films under different nitrogen-argon flow ratios were deposited on a sapphire (0001) substrate by RF reactive magnetron sputtering, and surface acoustic wave (SAW) filters were fabricated based on the ErAlN films. The results show that as the nitrogen-argon flow ratio increases, the crystalline quality and c-axis orientation of the film become better first and then worse, and the surface roughness decreases first and then increases. When the N2/Ar ratio is 12∶17, the ErAlN thin films own best crystal quality and minimal surface roughness. The SAW filter based on ErAlN film has a resonance effect between 273 MHz and 288 MHz, and when the N2/Ar ratio is 12∶17, the SAW filter has the smallest insertion loss and the largest transmission coefficient.