中文摘要：

分层削减公式是在多哈回合2004年的“七月框架协议”中确定的农产品关税削减的主要方式。本文提出了减让方案的评价准则，着重研究从三个递进的层级建立了农产品市场准入评价指标体系。并且以中国为例，分析和评价基于分层公式的美国、欧盟、G20和G10等减让方案对中国农产品市场准入效果的影响，提出了我国在多哈回合农产品谈判中的攻防策略。

英文摘要：

The Zipf law reflects the simple and elegant relationship between the sizes of cities and their locations, meanwhile it is also a important principle to study the urban agglomeration and the rationality of the urban system. This paper used the urban data of the provinces in China after reform and opening up to study the sizes of cities according to the Zipf law. The research showed that the Zipf index of urban size in China was not 1 significantly and increasing constantly .On this base , this paper used mixed OLS model and GLS panel model to analysis some influenting factors on the sizes and locations of the cities in China such as traffic conditions,level of industrialization, FDI, GDP per capita, urban population and