With the vertical velocity obtained by POM for simulating the circulation in the East China Seas, the upwelling and downwelling in the Changjiang River Mouth area are discussed. This simulation showed convincingly that upwelling exists in the area of the northern part of the Changjiang River Mouth; and that the downwelling which exists in its southern part which separates the upwelling at the Chang jiang River Mouth from the Men and Zhe coastal upwelling. This simulation showed that the upwelling at the Chang jiang River Mouth is caused by interaction of the Taiwan Warm Current with the slope bottom topography; and that southwest the monsoon in summer can strengthen the upwelling at the Changjiang River Mouth and the Men and Zhe coastal upwelling.