Abstract: A vertical one-dimensional water temperature and ice condition model and a longitudinal one-dimensional water temperature model have been developed in this study to explore the influence of reservoir construction on water temperature and ice conditions in the northwestern cold regions. These models were applied to a case study of the Huangcangsi reservoir and its downstream river channel, and different cases of reservoir operation were examined and compared with the natural condition. The results show that this reservoir is the type of thermal stratification with inversion profiles of its water temperature behind the dam in winter, and hence it produced certain effects of weakening ice formation. In comparison with the natural river, the start time of frazil ice was delayed by about one month; the lasting period of ice condition was cut down by roughly 20 days; the maximum ice thickness was reduced to 0.49 m from the corresponding value of 0.76 m in the natural condition. As a result, no ice condition was detected in a certain reach downstream of the dam, and in the sluicing occurred a phenomenon of lower water temperature in spring and summer and higher temperature in autumn and winter than those in the natural condition. And under the dam, monthly mean water temperature was recovering along the stretch to normal in different degrees.