Linear alkylbenzene sulfonates (LAS) are the most commonly-used anionic surfactants in cleaning agents and detergents. Taking sodium dodecyl benzene sulfonate (SDBS) as the target LAS, this study investigated the degradation and transformation of LAS in integrated constructed wetland–microbial fuel cell (CW–MFC) systems. Results showed that, SDBS was able to improve the power output and reduce the internal resistance of CW–MFCs by reducing transmembrane transfer resistance of organics and electrons because of the amphiphilicity and solubilization, however, SDBS with relatively high concentration had a great potential to inhibit electricity generation and organics biodegradation of CW–MFCs because of the toxic effects on microorganisms. C atoms on alkyl group and O atoms on sulfonic acid group of SDBS had greater electronegativity and were prone to oxidation reaction. The biodegradation of SDBS in CW–MFCs was a process of alkyl chain degradation, desulfonation and benzene ring cleavage in sequence via ω, β and/or α-oxidations and radical attacks under the action of coenzymes and oxygen, in which 19 intermediates were produced, including four anaerobic degradation products (toluene, phenol, cyclohexanone and acetic acid). Especially, for the first time cyclohexanone was detected during the biodegradation of LAS. The bioaccumulation potential of SDBS was greatly reduced through the degradation by CW–MFCs, and thus the environmental risk of SDBS was effectively reduced.