This dataset is the 2020 version of the national Secondary Forest Age Dataset for China (SFAC), generated based on 1986–2021 Landsat 5/7/8 time series data, combined with change detection algorithms such as VCT and CCDC, random forest (RF) model, and stacked generalization ensemble algorithm (VCR2). With a spatial resolution of 30 m and WGS-84 projection, the age range is 1–34 years, covering mainland China and Taiwan (excluding the South China Sea islands). It can be used in secondary forest resource surveys, forest carbon stock estimation, and ecosystem dynamic research in China, filling the gap of national-scale high-resolution secondary forest age data.