Abstract: According to the evolution of natural environment and the uplift of the Qinghai-Xizang Plateau in the Cenozic, the forming process of East Asia monsoon can be dividedinto four stages. 1. No-monsoon stage. In the Eogene period before the uplift of the plateau, there was no monsoon circulation in East Asia, therefore the climate in the area at that time should be the planetary winds. 2. Quasimonsoon stage. In the Neogene pe-riod when the plateau reached about 1000m, the positions and areas of Eurasia were as the same as those at present, and the quasimonsoon in East Asia began to form at that time. 3. Maritime monsoon stage. In the early period of the Quaternary the altitude of the Qinghai-Xizang Plateau was about 2000m, which made the summer monsoon of East Asia strong, and the climate in the area at that time was warmer and moister than that at present. 4. Continental monsoon stage. In 1, OMaB. P. the Qinghai-Xizang Plateau reached about 3000m, which made the winter monsoon stronger than the summer mon-soon in East Asia and the environmental evolution in the area tend to drier and colder, and the modern circulation pattern of continental monsoon in the area has formed since the middle period of the Quaternary.