Based on the general theory of positive externalities of farmland circulation,this paper proposes that positive externalities of farmland circulation are mainly refected in promoting agricultural modernization,rural urbanization and urbanization of farmers etc.In order to improve the positive externalities of farmland circulation,we should abide by the concept of balance and coordination of economic law,the principle of both optimal allocation of resources and the sustainable development so as to realize such objectives as economic efficiency,economic fairness and social harmony.In the practical level,this paper analyzes the beneficial experiences of the United States,Japan and France in positive externalities of farmland circulation,and puts forward the realization of law incentive of positive externalities in farmland circulation of China from legal system of property rights division,legal system of finance and taxation,legal system of financial credit and legal system of intermediary bodies.