Abstract: Through wide investigations, applying the principle of comparative advantage, this paper studys the farmers' desire in management of farmland. It considers that planting should go through the process in which farmers will take several occupations, in the course from the state of even division of farmlands to that of specialization with approprate scale of manageement. This paper states a calcutation method on the basis of which the economic critical value of the turning point can be determined. Using the above method, the authors have predicted the developing process of management with appropriate scale in main agricultural districts of Henan Province in different periods and conditions, and have analyzedt the main contradictions in different stages of the develop of planting. At the same time, this paper suggests the way to deal with the situation.