Abstract: The QDs modified with oleic acid is synthesized by the authors. It is lipophilic, of high-efficiency and oxygen insensitivity, and its emission(520 nm) overlaps the Q band absorption peak of Platinum(II) with octaethylporphyrin (PtOEP) as the reference. The sensing film is fabricated by using QDs doped with PtOEP which is encapsulated in plasticized polystyrene (PS). The sensor is used for direct mapping of the spatiotemporal variation in oxygen distribution within the effects of Enteromorpha Prolifera in littoral zone and bottom sediment. The result shows that high CO₂ may significantly enhance the respiration of Enteromorpha Prolifera, although the oxygen concentration by photosynthesis activity is not significantly changed (about 7 mg/L only). The Enteromorpha Prolifera begins to decay under high temperature and the peak of the oxygen concentration is then dropped to 2.3 mg/L. The decaying Enteromorpha Prolifera at the sediment -water interface forms a severe hypoxia zone in seawater around the sediment-water interface and the hypoxia zone has great impact on the marine environment.