The Asian summer monsoon circulation, especially its climatological seasonal change, was studied as the model response to the prescribed zonal mean field and the prescribed diabatic heat source from the observation. Climatological seasonal change from early summer (June) to mid-summer (July) is characterized by an air temperature increase in the whole Northern Hemisphere and a northern shift of weakened westerly jet. When in the model a zonal mean field in June is replaced by that in July, the major characteristics of the seasonal change are obtained qualitatively; low-level jets and upward motion areas in South Asia and East Asia shift from the ocean side of the coasts toward the land side. This change of vertical motion is consistent with the seasonal change of deep heat sources from June to July. The climatological seasonal change from mid-summer (July) to late summer (August) is characterized by enhanced convective activity in the extended area of the subtropical western Pacific. When deep heat sources in July are replaced by those in August over the western Pacific only, the major expansion of the Tibetan High at the upper-level and the Pacific High at low-level over Japan is also simulated by the seasonal change of the western Pacific heat sources only.