The novelty of this work is to explore the driving process and key environmental factors governing As mobilization mediated by DFeRB and SRB on the basis of continuous As speciation and environment parameters monitoring in sediment-water system. The results illustrated that DFeRB and SRB played a critical role in regulating As mobilization in sediment-overlying water system. The reduction process mediated by DFeRB and SRB significantly promotes reduction of As (V) and endogenous release of As. However, in the DFeRB and SRB mediated reduction, the main driving process and their key explanatory factors that dominated As mobility were obviously different. DFeRB presented significant effects on the reductive dissolution and re-distribution of Fe (III) oxyhydroxides and As-containing Fe (III) minerals as well as adsorption-desorption, which in turn influenced the transformation of iron species and the release and ecotoxicity of As. Significantly different form DFeRB, the effects of SRB on As behavior mainly by influencing adsorbed As, pyrite and As sulfides in sediment as well as the formation of sulfide during sulfate reduction. The main pathways on As mobilization were the direct effects of SRB, S2- and Fe2+. In addition, the role of NH4+-N for the driving process of As mobility is more pronounced for SRB-induced reduction. NO3--N is an essential factor affecting As mobility, but the effects of NO3--N on As was a non-significant pathways. This work is helpful to provide insight into the environmental effects of DFeRB and SRB on biogeochemical cycle of As.