In this investigation, four set of triple experiments which include with lake experiment, 3/4 lake experiment, 1/2 lake experiment, without lake experiment were conducted by using NCAR non-hydrostatic mesoscale model(MM5V3.7). The simulation results are reasonable compared with the observations data from Namco Monitoring and Research Station. The main result show:(1) Combined with the lake-land breeze and mountain-valley winds, in daytime, there is a clear shear line on the Mt.Nyainqentanglha in horizontal direction and a strong up flow in vertical direction, in nighttime, the whole area was controlled by south flow which provide the water vapor and support the day time instability movement.(2) The existence of lake has a strong cold(warm) lake effect to the summer atmospheric boundary layer characteristics over the lake Namco region in daytime(night).(3) Lake Namco has significant day change impact on sensible heat flux and latent heat flux. Both sensible heat flux and latent heat flux is small in day, and in night, there is strong latent heat flux over the lake.(4) Lake Namco makes atmospheric boundary layer height over the lake lower than the land.