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In terms of the NCAR Community Climate Model (CCM3), the effect of the Indian Peninsula on the course of the Asian tropical summer monsoon is simulated in this paper, and numerical experimental results show that the Indian Peninsula plays a critical role in the establishment process of the Asian tropical summer monsoon. When the CCM3 includes the Indian Peninsula,the model successfully simulates out the course of the Asian tropical summer monsoon, i.e. the South China Sea (SCS) summer monsoon at first bursts in middle May, while the Indian monsoon just establishes until middle June. However when the Indian Peninsula topography is deleted in the model, the Indian and SCS summer monsoons almost simultaneously establish in late May.Numerical results further indicate that in the former experiment the sensible heating of the Indian Peninsula warms the air above and produces evident temperature contrast between the peninsula and its adjacent SCS and Bay of Bengal (BOB), which results in the strengthening and maintenance of the BOB trough in the low-middle layer of the troposphere in the end of spring and early summer and thus the earliest establishment of the Asian tropical summer monsoon in the SCS in middle May. However, the Indian summer monsoon just establishes until middle June when the strong west wind over the Arabian Sea shifts northwards and cancels out the influence of the northwest flow behind the BOB trough. In the latter experiment the effect of Tibetan Plateau only produces a very weak BOB trough, and thus the SCS and Indian summer monsoons almost simultaneously establish.