The　electrodes　spacing　would　exert　a　pronounced　effect　on　bio-electrochemical　systems　(BESs)　performance,　especially　for　the　scaling-up　of　reactors　and　practical　applications.　In　this　study,　we　traced　the　effect　of　electrode　spacing　on　wastewater　treatment　performances　from　the　aspects　of　hydrodynamics　and　electrochemical　characteristics.　Three　series　of　folded　stainless　steel　mesh　(f-SSM)　electrodes　with　electrode　spacing　of　2,　4　and　8　mm　were　designed　for　azo　dye　(acid　orange　7　(AO7))　wastewater　treatment.　Results　showed　that　BES　with　electrode　spacing　of　2　mm　(R-S2)　obtained　the　highest　efficiencies　of　AO7　decolorization　(90.9　+/-　0.4%)　and　COD　removal　(36.8　+/-　3.8%)　at　HRT　of　8　h,　which　was　30.7%　and　15.2%　higher　than　that　in　BES　with　electrode　spacing　of　8　mm　(R-S8),　respectively.　Moreover,　the　relationship　between　pollutants　removal,　internal　resistance　and　hydrodynamics　of　BESs　with　different　electrode　spacing　supported　the　hydrodynamics　was　significantly　influence　the　pollutants　removal　performance.