The optical and mechanical properties and the microstructures of Nb2O5, Ta2O5 and SiO2 thin films prepared by the ion beam sputtering (IBS) method are studied. The effect of the assisted ion source voltage on the film properties is analyzed. The comparison among films prepared by the electron beam evaporation, ion beam assisted deposition and IBS is also conducted. The study results show that the films prepared by IBS possess better optical performance and microstructures, as well as higher compressive stress, hardness and Young modulus. The assisted ion source is beneficial to improving the optical performance, adjusting the film stress and reducing the surface roughness of thin films, however, it has relatively small influence on the hardness and the Young modulus. Under different assisted ion source voltages, the stress of prepared Nb2O5 by IBS is -152--281 MPa, that of Ta2O5 is -299--373 MPa and that of SiO2 is -427--577 MPa. Under proper process parameters, the extinction coefficient can be smaller than 10 -4 and the film surface is smooth with a root mean square roughness of smaller than 0.2 nm.