Abstract: The Taihu Watershed belongs to the eastcoastal developed area in China. In 2000 the level of urbanization was 66.17%, near twice of the average urbanization level in China. Since the opendoor policy the region has been proceeding with rapid industrialization, from the countryside industry develop to the foreign investment industry. The affluent job opportunities in these new factories have attracted a huge immigratory population from all over the country. Hence immigration becomes an important element affecting regional development plan. With the data provided by the fifth population census this paper analyzed the regional composition and urbanrural composition of immigration, calculated the number of immigra tion and its distribution by cities (counties) in the Taihu Watershed. The immigration contributed to around two percent of the level of urbanization due to its unbalanced distribution between the rural and urban areas. For the total city population, immigration occupied about 18% on average. The proportion of immigration was significantly linearly correlated with city population size in cities with over 500 000 population, and the proportion was significantly correlated with GDP in cities with less 500 000 population. The results should be useful for the prediction of urban population size of the cities and for the prediction of regional urbanization level in the Taihu Watershed, and could provide references for other cities or regions with the similar social and economic situation.

Key words: the Taihu Watershed, level of urbanization, immigratory population