The structural analysis of amorphous carbon films is not only the premise of their unique properties applied in the industrial fields but also the indispensable element on their classification. In this letter, we refurbished the classification of amorphous carbon films based on the optical constants in terms of the refractive index (n) and the extinction coefficient (k). In the selected photon energy range, we defined the maximum of n (En-max) and k at a value more than 10(-4) (E-k) to explore the relationship between different classification schemes for amorphous carbon films deposited by different techniques. We found that Ek and En-max of the deposited amorphous carbon films have an exponential relationship with the hydrogen contents. Thus, the spectroscopic ellipsometry analysis can also be used as one of the effective methods for the structural evaluation of the amorphous carbon films. (C) 2017 Author(s).