The differences were described between city and countryside from different levels in this article, became into being the conjuncture consciousness of unbalanced relation between city and countryside, understood the inevitability of city and countryside plan as a whole. It is a material embodiment of the rules that production relation must adapt to develop level of the productivity, it's an impersonal demand for deploying resource as perfect or effective as possible; And search the international experience of city and countryside harmonious development plan as a whole, bring up countermeasure and measure which can solve problem of " Sannong" Prominently and it is break the division system of city and countryside to boost up the ability of city and countryside harmonious development plan as a whole ,and realize the relations of equal, moderate, blend, development between city and countryside by posting the main reasons that caused differences of the city and the countryside and these reasons are the policy of dualistic economy structure was executed by China government in a long time at past.