A three-dimensional (3-D) hydrodynamic model based on Princeton Ocean Model (POM) and a one-dimensional (1-D) lake model are applied to simulate the thermal structure and circulations of Lake Nam Co (LNC), the second largest lake in Tibet. Results show that POM can well reproduce the seasonal and synoptic variations of the in-situ observed vertical temperature profile, and the spatial distribution of satellite estimated lake surface temperature during May-December 2013. However, without considering the water and energy exchanges related to the lake hydrodynamics, the 1-D model exhibits much more evident biases in the lake thermal evolution. These shortages of the 1-D lake model solutions emphasize that the complex temperature-current interactions must be accounted for investigating the thermodynamics in large lakes over Tibet. From both observation and hydrodynamic simulations, LNC is identified to experience the springtime overturning, warm stratified phase during early-June to mid-November, autumnal overturning, and weak inverse stratified phase since mid-December. The two overturning processes last for about one month and are both related to the thermal bar development, which is controlled by the density-driven convection associated with the radiative heating (surface cooling) in spring (autumn). During the warm stratified phase, the eastern shallow basin is mainly characterized by anticyclonic circulation and bowl-shaped thermocline, while the central deep basin is featured by a cyclonic gyre (eastward currents) and dome-shaped (bowl-shaped) thermocline with the enhancement (weakness) of thermal stratification. The lake circulation during December is basically dominated by a single strong cyclonic gyre in the main lake basin.