Marine dissolved organic matter (DOM) plays an important role in the microbial carbon pump. Understanding the degradability (i.e. degradation state) of marine DOM can help us understand and predict the tendency of marine organic carbon reservoir. There are usually algal blooms and hypoxia events in the Yangtze River estuary because of human activities and special hydrological conditions. When these events occur, there are organic matter degradation and thus  oxygen consumption. How does reduced oxygen further impact DOM degradation? To clarify this question, a field investigation was conducted in the northern sea area off the Yangtze River estuary in October 2021 to characterize the DOM degradability via amino acids. We find that AOU (0.06 - 2.13mg/L) and DI values (-0.78 - 2.84) were significantly positively correlated in bottom water (r=0.87, p=0.001, n=10). The correlation analysis of bacteria relative abundance at family taxonomy level with both DI and dissolved oxygen (4.7 - 7.4 mg/L) shows that almost all families that negatively correlated with DO were positively correlated with DI significantly, indicating that DO may affect DOM degradation by regulating microbial composition. Further analysis of microbial composition suggests that, when the DO concentration is low, the microorganism can reduce the degradation of DOM and the release of CO₂ by changing the community composition towards the anaerobic and facultative anaerobic dominated group, such as Lactobacillaceae. This study provides new insights into the impact of DO on DOM degradation.