Abstract: The phenomenon of the bifurcation of the strong large scale low-level westerly in East Asia in early summer is simulated with a five-layer primitive equations model. The physical mechanism for forming the bifurcation of the strong low-level westerly and the corresponding subtropical monsoon rain belt and tropical monsoon rain belt is explained further. The simulated results will be beneficial to the forecasting of the Mei-Yu in the middle-lower reaches of the Yangtze River and precipitation in the South China Sea Waters.