The ocean is the largest source of NO emissions from global aquatic ecosystems. However, the NO production-consumption mechanism and microbial spatial distribution are still unclear. Our study established a bottom-up model based on the source‒sink boundary and the microbial sources of NO. A high-resolution (0.1°) global distribution of oceanic NO was depicted, confirmed by approximately 150,000 surface measurements. The microbial NO flux is 2.9 Tg/yr N-NO, with the oxygen-deficient zones (ODZs) disproportionately accounting for more than half of the total emission. High primary productivity, sharp oxyclines, and shallow emission depths caused the ODZs to be NO hotspots. Geographically, ammonia-oxidizing archaea (AOA, 1.0 Tg) are the most widely distributed contributors to NO emissions in the ocean, completely overtaking ammonia-oxidizing bacteria (AOB). Heterotrophic denitrification, mainly occurring in ODZs, contributes the most (1.6 Tg) to NO emissions. Overall, this study offers a bottom-up framework for understanding microbial source-sink mechanism in the ocean.