Abstract: Including detailed physical processes, a three dimensional model was used to simulate mesoscale ciculation of the Dianchi lake, Yunnan province.The simulation result was basically accordant with observation data. The area of Dianchi, divided into parts of lakes, mountains, basins and hills, features on a cool center over the lake in daytime and a warm center at night; vertical circulation is stronger in daytime than at night and lake breeze, which is much affected by regime winds, effects much wider influence than land breeze does. It provided some scientific basis for the research of atmospheric boundary layer stracture and crucial reference for enviroment quality assessment.