Ultrathin tetrahedral amorphous carbon (ta-C) films with different film thickness were prepared by filtered cathodic vacuum arc technique. The accurate measurement of the film thickness and sp³C content of the ultrathin ta-C films was conducted by means of ellipsometry combined with spectrophotometry. The acquired film thickness was further verified by XRD. The film density was acquired from the results of precise determination of lattice parameters. Raman spectroscopy were conducted to characterize the atomic bond structure of as-prepared film. The residual stress was calculated from the curvature of the film/substrate composite using Stoney^，s equation. Results show that as the film thickness increased from 7.6 to 33.0 nm there was no obvious change of the ultrathin ta-C film growth rate, which keeps constant as 1.7±0.1 nm/min, while the residual compressive stress and sp³ fraction decreased; for the film of thickness 7.6 nm the maximal sp³ fraction was obtained. The results are consistent with Raman's. For the film of thickness 11.0 nm, the maximal bulk layer density was 3070 kg/m³. The film thickness had no obvious influence on surface roughness of ultrathin ta-C films. In summary, ellipsometry combined with spectrophotometry is of feasible means for characterizing the structure and thickness of the ultrathin ta-C films. X-ray reflection can be used to measure the density and surface roughness of ultrathin ta-C carbon films of high quality.