Abstract: Water temperature（WT） and dissolved oxygen（DO） are important parameters to characterize the healthy status of an aquatic ecosystem. This study develops a three-dimensional model of water temperature and dissolved oxygen in the Guanting Reservoir（GTR） to quantify the impact of its ecological regulation. This model is calibrated and verified against on-site measured data, demonstrating its capability of predicting the reservoir’s temperature and oxygen conditions. Combined with real reservoir operation, different scenarios are designed to analyze structural changes in WT and DO in the reservoir area.（1） The simulations show obvious WT and DO stratification in GTR. Water transfer operation causes a delay in stratification start time and a decrease in stratification duration and surfacebottom temperature difference, while ecological discharge brings about a further decrease in the thickness and intensity of thermocline up to the variation ranges of 0.5-1.7 m and 1.25-3.58℃/m respectively. Simultaneous operation of the transfer and discharge strengthens water body mixing in the reservoir, resulting in an increase in the thermocline depth up to an average range of 6.2-8.6 m, an increase in thermocline intensity, and a slight change in thermocline thickness.（2） Either water transfer or ecological discharge will damage the oxycline of water body and has a significant effect of increasing oxygen content in the bottom layer, but its effect on the surface DO that varies in a range of-4.7% to 7.3% is insignificant.（3） DO concentration in the bottom water is increased by 1.85-8.52 mg/L under the operation of ecological discharge only, while increased by 2.71-12.83 mg/L under both the transfer and discharge, producing more prominent oxygen enriching effect. This will eliminate the anaerobic environment in the reservoir bottom layer, reduce the low oxygen area, and prolong the oxygen rich period, revealing significant measures for improving anoxic environment in lakes and reservoirs.