Abstract: Water column samples taken from the northern and the southern lake centers in Hongfeng lake in summer stratification were measured about their water temperature,pH,the concentration of HCO₃^-,DO,Chla,NH₄⁺,NO₃^-,and PO₄^3-.The pressure of CO₂ (pCO₂) was calculated by the chemical balance and the Henry's law.The results show that the photosynthesis,the degradation of the organic matter and the thermal stratification are the main factors regulating the distribution of pCO₂ in Hongfeng lake.The unsaturation of CO₂ in the epilimnion is caused by the fixation of CO₂ during the photosynthesis and the sharp increase of CO₂ in the metalimnion may be due to the degradation of the photosynthesis production.In addition,the pCO₂ in the hypolimnion near the sediment is the highest and has an increasing tendency,which indicates that the degradation of organic matter in the sediments has an important effect on the pCO₂ in the hypolimnion.The thermal stratification results in the significant variation of pCO₂ in the water column and the accumulation of CO₂ in the hypolimnion.Finally,the variation of pCO₂ is concomitant with the variation of the nutriments:the consumption of nutriments during the photosynthesis took place in the upper water column and the release of nutriments during the degradation of the organic matter in the lower water column.