Culturally protected forests, which are preserved and managed by local people on the basis of traditional cultural practices and beliefs, have certain social and ecological functions, and also show significant role in biodiversity conservation. The research worldwide nowadays mainly focuses on qualitative description of culturally protected forests and therefore lack quantitative comparison of biodiversity and difference in species composition between culturally protected forests and non-culturally protected forests, particularly diversity from different spatial scales. The tree layer, shrub layer, herb layer and vine layer of three culturally protected forests and non-culturally protected forests were investigated, using additive partition measured by species abundance to analyze diversity of multi-scale in subtropical region of China. Partitioning of total species diversity can be described as Alpha diversity (within grid diversity)+ Beta diversity= Gamma diversity (total diversity at landscape), among which Beta diversity could be divided into diversity between grids, diversity between plots, diversity between forest types. The results were: (1) Total 296 species belonging to 66 families and 163 genera were found in culturally protected forests, dominated by Castanopsis sclerophylla, Cinnamomum camphora and Castanopsis carlesii, while 189 species belonging to 67 families and 135 genera were found in non-culturally protected forests, dominated by Cunninghamia lanceolata, Pinus massoniana and Phyllostachys heterocycla cv. pubescens. Culturally protected forests had more species in tree layer and shrub layer although the differences of species composition were complex in herb and vine layer depending on human disturbance and locations, and most of species diversity was higher in culturally protected forests. (2) This model implied that Beta diversity was increasing at larger spatial scale, and which showed uniform results in different layers in both culturally protected forests and non-culturally protected forests. Additive partitioning of diversity between forest types was highest which was from 41.9% to 62.8% of total diversity at landscape level, followed by diversity between plots which was from 18.6% to 31.9%, the contribution of diversity within and between grids was only small proportion. (3)Culturally protected forests play dominant role in partitioning of diversity between forests types, and provided 54.4% to 81.0%, 51.2% to 60.2%, 42.9% to 64.1%, 49.9% to 62.2% of total diversity in culturally protected forests and non-culturally protected forests in tree, shrub, herb and vine layers respectively. That means culturally protected forests act as species pool to the regional area, particularly in conservation of tree species. (4) Species accumulation curves of tree layer achieved smooth slower indicating larger number stands protected in culturally protected forests than non-culturally protected forests within the same sample area. Additive partitioning of species diversity offers an operational method for explaining species diversity and in terms of better understanding of how alpha and Beta diversity change across multiple spatial scales. The model suggests culturally protected forests could be key factor to make contribution for diversity at landscape level. Therefore, when making biodiversity protection and restoration strategies, it's better to focus more on culturally protected forests. However, the impact of human disturbance to culturally protected forests still needs to be studied in depth.