Population numbers of four tuber-eating bird species(Grus leucogeranus, Grus vipio, Anser cygnoides and Cygnus columbianus) were surveyed and water levels were recorded to analyze the relationships between changing water levels and bird population numbers in Poyang Lake National Nature Reserve. During the winters(from October to next March) of 2003-2007, the population numbers of the four tuber-eating birds were surveyed by direct counting method, and the relationship between water levels and population numbers was analyzed by using non-parametric regression method in SAS. The results showed that the changes of population numbers of the four species with the fallen of water levels appeared consistent. With sustainable fall of water level, the bird population first increased and then declined showing an inverted V-shape. When water level changed from 16.0 m to 14.8 m(Wusong Elevation), the population numbers increased with the fall of water level. However, the bird population decreased when water level fell from 14.8 m to 13.5 m. Higher population numbers occurred at water levels between 14.5 m and 15.5 m. The highest population number occurred at about 14.8 m. The changes of population numbers of 2003-2005 in the winter showed similar unimodal patterns, with highest numbers occurred at 14.75-14.90 m. In the winter of 2006 and 2007, with the rise of the average water levels, the water level of peak population numbers rose, occurred at about 15.25 m. The relationship of water levels and population numbers were relatively stable at Dahuchi and Shahu, for these two lakes were under well protected, while in Meixihu, there was no significant trend in the changes of population numbers and water levels. The result helps guiding the water level management for Poyang Lake National Nature Reserve.