中文摘要：

本文强调两个事实：第一，农村居民并非同质，他们根据自身的特征决定迁移与否；第二，那些成功地改变了户籍身份的永久移民与没能改变户籍身份的临时移民之间有着显著的差异。利用2002年的CHIP数据发现，永久移民的“正选择”效应非常明显，它使得农村地区教育水平较高、处于收入分布较高位置的样本减少。这导致农村的收入水平和农村内部的不平等程度降低，阻碍了城乡差距的降低。相反，临时移民的选择效应几乎可以忽略不计。

英文摘要：

In this paper, we emphasize two facts. First, rural residents are not homogeneous, they self-seleet to migrate or stay home. Second, there are significant differences between migrants who have successfully obtained urban hukou （permanent migrants） and those who have not （temporary migrants）. Using the 2002 CHIP data, we find that permanent migrants are positively selected from rural population. As permanent migration occurs more in the upper half of rural income distribution, both average rural income and inequality decrease, and the urban-rural income gap increases. On the contrary, the selection effect of temporary migrants is almost negligible.