Background:　Advanced-Flow　Reactor　(AFR)　can　produce　excellent　mixing　and　is　proven　to　be　highly　efficient　and　easy　to　expand,　which　is　closely　related　to　the　fluid　flow　characteristics.　Method:　The　visualization　experimental　study　was　carried　out　to　study　the　behavior　and　mechanism　of　the　bubble　breakup　in　a　single　Corning　G1　module.　Significant　findings:　The　results　showed　that　the　breakup　behavior　in　AFR　had　a　significant　regularity　at　low　Reynolds　numbers　(Re<1000).　The　breakup　behavior　was　closely　related　to　the　capillary　number　Ca　and　the　virtual　length　l0　of　bubbles,　and　the　criterions　was　also　obtained.　Most　of　bubbles　in　arc-shaped　junction　divergence　of　AFR　were　breakup　with　permanent　obstruction　(POB),　which　could　be　divided　into　two　stages:　squeezing　stage　and　rapid　pinch-off　stage.　The　modified　equation　obtained　in　this　paper　can　roughly　describe　the　change　of　the　bubble　neck　at　the　squeezing　stage　of　POB.　The　research　results　provide　a　theoretical　basis　for　industrial　application　of　AFR　and　the　development　of　next-generation　reactors.　©　2022