A reliable and accurate method based on multilayer film model by spectroscopic ellipsometry is proposed to measure optical constants of UV weak absorption films. Take examples of HfO2 film and SiO2 film, multi-angle ellipsometry parameters Psi and Delta had been measured by spectroscopic ellipsometry to inverse optical constants of HfO2 and SiO2 film between 200 nm and 900 nm in Wavelength, which were fitted by point-by-point method using the Cauchy with urbach absorption model. Comparing the fitting result of ellipsometry and the test result of scanning electron microscopy (SEM), we verified the accuracy of the optical constants of HfO2 and SiO2 film. The results show that the structure and optical constants of weak absorption coating can be better described by Cauchy with urbach absorption model using point-by-point method, and the results are important for the fabrication of UV filters.