A numerical model coupling atmosphere with hybrodynamics is set up in this paper to study the gyres mechanism m Lake Biwa, Japan. Some results arc obtained as follows:1)There exists a positive wind vorticity field over the lake, and also a positive wind divergence field in daytime and negative one in night This special atmospheric boundary layer of Lake Biwa catchment can generate a typical land-lake breeze, this local wind system can induce and maintain a weak but stable counter-clockwise gyre in north lake during period of thermal stratification. 2)When considering inbomogeneous wind field. the gyres formed in the lake can sustain longer and be more stable than that only driven by homogeous wind over the lake. 3)The local wind system can produce a typical horizontal distribution of water temperature, i.e. water temperature higher in shallow water, lower in deep water.