Abstract: By using the numerical experiment, the influence of thermal contrasts between Africa and Arabian Sea, Indian Subcontinent and Bay of Bengal, Indochina Peninsula and South China Sea on the formation of Asian summer monsoon are studied. The results show that not only the thermal contrast between Asia continent and its surrounding ocean influence the summer monsoon formation, but the thermal contrasts between subplanetary scale ocean and continent mentioned above can also influence the structure of summer monsoon. The velocity centers of southwest monsoon over the Arabian Sea, Bay of Bengal and South China Sea and their cross-equator currents are produced by the effect of thermal contrast.