Abstract: The concept of "Benefit Limited Reclamation Area" is put forward for the first time in this paper. The function relation between economic benefit and the reclamation area can be approximated by a quadratic function. In a given sea area, it is assumed that the reclamation project generally is implemented from the shallow water to deep water step by step with the increase in cost of the unit area as the depth goes deeper in the sea. When the depth reaches to a certain level, economic benefit will no longer rise even if the reclamation area still extends. When achieving its peak, the economic benefit over the reclamation area is called the Benefit Limited Reclamation Area. . If the area exceeds the limit value, the economic benefit will decrease but not increase when reclamation proceeds into deeper water. The viewpoint of the larger the better the reclamation area is not true, and the area is controlled by the Benefit Limited Reclamation Area. Therefore, it is very necessary to control the reclamation area adequately.