TiO₂-Ta₂O₅ thin films are new-style optical thin films which are made of mixed compounds as starting material.The TiO₂-Ta₂O₅ compound thin films were fabricated by ion beam assisted deposition on K9 glasses with Ta₂O₅ and TiO₂ of different proportioning as starting materials,and the optical properties were investigated.The testing results show that TiO₂-Ta₂O₅ thin films have the higher transmittance and the lower extinction coefficient at visible light wavelength,and the refractive index varies from 1.80 to 2.07(550nm).TiO₂-Ta₂O₅ thin films are of great significance in optical fields.The optical band gap of TiO₂-Ta₂O₅ films increase from 3.266eV to 3.417eV while the content of Ta₂O₅ enhances from 0 to 20%,and the shift of absorption edges in transmittance spectrum is explained by Kayanuma model.