Abstract: Based on the survey data of the South Yellow Sea section in August of 1977 to 2016, the spatial and temporal evolution and mechanism of hypoxia and anoxia were studied by spatio-temporal analysis etc. The results show that the interannual changes of dissolved oxygen content and apparent oxygen utilization have 4 main spatio-temporal modes. The first mode of dissolved oxygen content and the first and the second mode of apparent oxygen utilization are the main influence components of the trend of the significant linear hypoxia and anoxia in the sectional areas. The second to the fourth mode of dissolved oxygen content and the third and the fourth mode of apparent oxygen utilization are the longterm variations of the quasiequilibrium state. The main mechanism of the summer hypoxia and anoxia changes in the South Yellow Sea is the increase and enhancement of the oxygen consumption process of the bioactive component (BAC). The main mechanism of longterm hypoxia and anoxia is that the effect of oxygen enrichment and oxygen reduction, due to the bioactive components, saturated dissolved oxygen and ocean current transport, is in quasiequilibrium state. The mean dissolved oxygen content and apparent oxygen utilization in the Yellow Sea cold water mass appears a significant linear trend of hypoxia and anoxia. The intensity of seaair oxygen flux in the sea surface in the South Yellow Sea in summer is linearly decreased and the “oxygen source” and “oxygen sink” change interactionally. The summer winddriven circulation and seaair oxygen flux gradually weakened in the Yellow Sea, which provides physical conditions for the development of summer hypoxia and anoxia in the Yellow Sea. The temporal and spatial distribution of the seasonal cycle of dissolved oxygen content and apparent oxygen utilization field in the Yellow Sea has been significantly changed in recent years.