The present situation, causes of formations and damages of soil erosion in Hanshui river valley in Nanyang city are analyzed, which is in the source area of the Middle Line Project of Transferring Water from the South to the North. The measures to control soiler osion in the area are disicussed. The serious soil erosion will have influence on the Middle Line Project . The reasons of soil erosion are natural factors and human factors such as overpopulation pressure caused by the emigrants returning back to the original districts. The countermeasures of soil erosion control include polit ical, economic, legislative measures as well as the way of settling emigrants appropriately.