The water temperature structure of reservoir is influenced by meteorological elements and inflow temperature, and presents regular change over a year. But the law of its daily variation is relatively lack. Based on Longtan reservoir, a prototype observation in front of the dam, which was divided into six stages, was performed from November 2011 to September 2012. The data analysis results showed that water temperature stratification is relatively stable during the observation period except January, and double thermocline was observed in July and September; The surface temperature had a big variation, while the bottom temperature was relatively stable throughout the year; The influence scope of meteorological elements on the water temperature in front of the dam was related to the season. In summer the reservoir water impacted by the meteorological elements was deeper than the others. The higher the temperature was, the earlier the maximum temperature appeared. Air temperature and solar radiation were the main factors affecting the diurnal variations of the structure of water temperature. In addition, the daily significantly change area of water temperature structure was only within 20m of the surface, which indicted that the diurnal change of surface water temperature hardly affected the temperature of discharge water.
