Abstract: We examined biomass characteristics and the potential driving factors of different forest types of Quercus spp. secondary forest in Hunan. A total of fifty plots were divided into five forest types: Castanopsis eyri - Rhododendron latoucheae mixed forest (CR), Fagus lucida - Fargesia spathacea mixed forest (FF), Lithocarpus glaber - Damnacanthus indicus + Camellia japonica mixed forest (LDC), C. eyri + Quercus serrata - R. latoucheae mixed forest (CQR), Cyclobalanopsis glauca - Camellia oleifera + R. latoucheae mixed forest (CCR). The biomass of understory vegetation was low in the five forest types, being smaller than 2.3 t·hm^-2. There was no significant difference in the biomass of understory shrubs among the five forest types. The biomass of herbage layer in CR was significantly lower than that of the other four forest types. The factors affecting the biomass of understory vegetation varied in different forests types. In CR, biomass of herbaceous layer was negatively correlated with canopy and uniform angle index, whereas total understory biomass was positively correlated with opening degree index. In FF, biomass of shrub layer was negatively correlated with stand canopy density and uniform angle index, while herbaceous biomass and total understory biomass were positively correlated with stand closure. In LDC, herbaceous biomass was positively correlated with the stand aggregation index. In CQR, shrub biomass was negatively correlated with stand mingling index, while herbaceous biomass was positively related with stand density. In CCR, there was no significant correlation between stand structure and understory biomass. To adjust the understory biomass, we should first adjust the horizontal distribution pattern of stand and then adjust the degree of forest cover and tree species structure.