Asian monsoon is a planetary-scale climate system driven by differences in heat capacity between the Asian Continent and its surrounding ocean. In boreal summer, a large-scale thermal low system appears on the Asian Continent, leading to change wind direction from ocean to the continent; note that wind direction is from the continent to ocean in boreal winter. Corresponding to this change in the wind direction, rainy season begins in most region in Asia, e.g., the rainy season is known as Baiu in Japan in early summer. For improvement of the prediction of the summer precipitation in Japan, and for prediction of the precipitation change in the future climate, our research team develop a Large Eddy Simulation model (SCALE-LES). This talk introduces a series of studies related to the Asian summer monsoon. At the same time, the treatment of lower boundary condition in the SCALE-LES, which is a crucial issue of our studies, is discussed.