The loess plateau becomes famous for serious soil erosion,which has directly influenced agricultural production and security of people's lives and properties of this area,and also influenced the development of the whole national economy.Through analyzing the origin reason of the loess plateau,the economic effects,the ecological effects and social effect of the loess plateau are appraised on basis of the policy of national conversing farmland to forest and grass land.The focal point is in terms of input and output to comparatively analyze the economic effects of conversing farmland to forest and grass land in the loess plateau that take routine seeds as an example.Thus some policies and suggestions are put forward.