Abstract: To explore the response relationship between the improvement effect of the stoplog gate and the stratification conditions of the water temperature upstream from the dam and its ecological effects on downstream fish reproduction, a two-dimensional water temperature model of the Wudongde Reservoir area was established based on the CE-QUAL-W2 model. A dynamic simulation of the water temperature under typical selective withdrawal conditions was carried out. The results revealed that under the nonselective withdrawal scenario of Wudongde Reservoir, the discharge temperature from April to May was 0～1.3 °C lower than the natural water temperature. After the stoplog gate was adopted, the daily improvement range was 0.2～1.2 ℃, and the proportion of the water temperature suitability index for the representative fish species（Rhinogobio ventralis）increased from 33.5% to 65.0%. When the water temperature improvement range was 0.6～1.0 ℃, the vertical temperature difference and stratification stability index needed to reach 6.2～8.3 ℃ and 556.9～ 1036.8 kg/m², respectively, and the stoplog gate needed to be continuously operated until early April. This study reveals the quantitative relationship between the strength of water temperature stratification and the effects of stoplog gates, providing a scientific basis for the optimization of stratified water intake scheduling schemes for large reservoirs such as Wudongde Reservoir.