A reservoir with branches was selected in Xinjiang Uygur Autonomous Region as the study subject． Based on the analysis of the interaction between branches and the reservoir，this study simulated the temperature dynamics in the reservoir under the scenarios with and without the influence of branches using 3D temperature model． The temperature distributions on reservoir water surface，in discharged water，and in the vertical profiles in upstream front of the dam were compared． The results show that the branches had certain influences on the temperature distribution of the reservoir; under the influence，the water in the bottom of the vertical profile in front of the dam had low temperature，as well as the discharged water from the dam outlet． The large temperature differences were found in the winter． Through shifting the location where the branches merge into the reservoir，the simulation indicated that the influences of the branches on reservoir temperature distribution increased as the merging point moving towards the dam．