Since its first release in 2004, the CAS Journal Ranking, a ranking system of journals based on a citation impact indicator, has been widely used both in selecting journals when submitting manuscripts and in conducting research evaluation in China. This paper introduces an upgraded version of the CAS Journal Ranking released in 2020 and the corresponding improvements. We will discuss the following improvements: a) the CWTS paper-level classification system, a fine-grained classification system utilized for field normalization; b) the Field Normalized Citation Success Index (FNCSI), an indicator that is robust against not only extremely highly cited publications but also wrongly assigned document types; and c) document type difference. In addition, this paper will present part of the ranking results and an interpretation of the features of the FNCSI indicator.