Abstract: During the sediment discharge period of a sandy river reservoir, a significant volume of low-temperature water is discharged along with the sediment. The outflow discharge can alter the downstream water temperature, potentially impacting aquatic organisms and their habitats. To investigate the evolution of downstream water temperature during the sediment discharge period, this research developed a refined heat exchange coefficient and established a one-dimensional unsteady water-sediment-temperature coupled mathematical model. Taking Xiaolangdi Reservoir as an example, a simulation and analysis of the downstream water temperature conduction processes during the sediment discharge period was performed. The results indicate: ①The outflow water temperature is the primary factor influencing downstream water temperature during the sediment discharge period, with the outflow water having a more substantial impact downstream as the discharge flow increases and sediment concentration decreases. ②The sensitivity of downstream water temperature to the outflow water temperature diminishes along the river, and the temperature change at the Lijin section is only 27.5% of that at the Huayuankou section in the same scenario. ③The sensitivity of downstream water temperature to the outflow discharge and sediment concentration increases initially and then decreases along the river, with the former reaching its maximum at the Aishan section and the latter reaching its maximum at the Jiahetan section. ④Both outflow discharge and sediment concentration have a comparable impact on downstream water temperature. Under the existing sediment discharge scheduling program of Xiaolangdi Reservoir, the maximum effect on downstream water temperature by outflow discharge and sediment concentration is approximately 2 ℃ each.