The origin of the modern-like East Asian monsoon has attracted much attention. It is debated as to whether the modern-like East Asian monsoon formed during the late Oligocene-early Miocene or the (late) Eocene. Resolving this dispute requires a comprehensive and updated synthesis of available geological records and a reliable modelling study. Here, we investigate Cenozoic climate patterns over East Asia by compiling geological records and conducting climate modelling based on our improved paleogeographies. Geological records suggest that a zonal (semi-)arid climate pattern was predominant over tectonic timescales across most parts of East Asia during much of the Paleogene, with significant dry-wet oscillations over orbital timescales, and a modern-like monsoon-dominated climate pattern has been established since the late Oligocene-early Miocene (ca. 28-22 Ma). This major climate reorganization was likely stepwise changes during similar to 28-22 Ma rather than occurring suddenly. Our simulations indicate that a zonal dry belt extended from western to central-eastern East Asia, except for coastal areas, during the late Eocene, and that a monsoon-dominated pattern had already formed over East Asia by the early Miocene. In addition, our simulations further indicate that East Asian rainfall is highly sensitive to orbital forcing and is also affected by pCO(2), which can explain the seemingly unstable character (i.e., dry-wet fluctuations) of the dry belt across East Asia during the Paleogene, reconciling previously conflicting wet and dry paleoclimatic indicators in East Asia during this period. Our results indicate that the dry belt did not necessarily constitute a continuous desert or desert-steppe landscape extending from the western interior to the eastern coastal region, but rather exhibited a certain east-west humidity gradient, with the eastern coastal region being relatively more humid, likely due to the influence of the weak summer southwesterlies along the eastern coastal region of China. Furthermore, our results suggest that paleogeographic changes, particularly uplift of the Tibetan Plateau to moderate-high elevations and its paleolatitude approaching present-day location during the late Oligocene-early Miocene, played a crucial role in the establishment of the modern-like East Asian monsoon, rather than pCO(2) levels.