The relationship between dissolved oxygen and nutrient cycle in low-wetland fishponds of the Huanghe-Huaihe-Haihe plain was studied. The results show that:1) The dissolved oxygen content depended on the photosynthesis of algae and the consumption of other organisms, which can be significantly improved by mixing. 2) The heterotrophic bacteria number of pond water was correlation with organic matter in addition to the dissolved oxygen. This change was more clearly especially in the sediments. 3) The dissolved oxygen of pond water significantly affected the changes of ammonification intensity and phosphorous decomposition intensity. When the dissolved oxygen was increased, the heterotrophic bacteria number and active were also improved, which caused the ammonification intensity and phosphorous decomposition intensity was significantly increased. This situation was more clearly in the sediments. 4) The nitrate reduction intensity and sulfate reduction intensity was negative correlation with the dissolved oxygen content. When the dissolved oxygen was decreased, the nitrate reduction intensity and sulfate reduction intensity were significantly increased. This situation also was more clearly in the sediments.