This　study　explores　the　enhancement　effect　and　the　underlying　mechanism　of　anthraquinone　2-sulfonate　sodium　salt（AQS）as　an　external　electron　mediator　in　the　degradation　of　Congo　red　by　photosynthetic　bacteria（PSB）.　The　results　show　that　the　optimal　dosage　of　PSB　and　AQS　was　50　mL（A=1.8）and　0.05　mmol·L-1，respectively.　It　was　found　that　the　addition　of　AQS　in　the　PSB　system　can　enhance　the　decolorization　and　degradation　of　Congo　red.　when　0.05　mmol·L-1　AQS　was　added　initially，The　average　decolorization　rate　of　Congo　red　reached　3.63%　h-1　which　was　2.47　-fold　higher　than　that　of　control　group.　The　addition　of　AQS　can　alleviate　the　inhibitory　effect　of　rotenone　on　azo　reductive　dehydrogenase，as　well　as　dicoumarin　on　quinone　reductase.　AQS，as　an　oxidation-reduction　intermediate，transferred　electrons　for　the　degradation　of　azo　dyes，and　enhanced　the　degradation　rate.　©　2025　Science　Press.　All　rights　reserved.