To understand the temporal and spatial variation of heat conditions in a large reservoir of a cold region, a prototype observation in the Fengman reservoir was performed to investigate the water temperature and ice conditions from June 2010 to August 2011. Based on the data, the annual heat structural variation of the water temperature in the reservoir was elaborated, the effect of the flood process on the layered water temperature structure was analyzed, and the buoyancy flow on the surface layer in the early period of the thawing season was observed. The vertical water temperature structures, 75 ~800 m in front of the Fengman dam, are almost the same in June and July, and the slight difference between the discharge temperature and the average water temperature in the water intake elevation indicates that the three-dimensional effect in front of the dam is non-existent. Influenced by the deep water intake, the temperature of the discharge is stable, while in contrast with the natural water temperature, the mean discharge temperature can be 10.8℃ lower from May to July and 7.9℃ higher from October to December. In addition, the ice condition observation results indicate that the Fengman reservoir is ice covered during the entire winter and that the maximum value of ice thickness reaches 0.7 m; meanwhile, the distribution of the ice thickness is uneven during the icebound season.