Stable isotope techniques have been increasingly used to assess the structure and function of freshwater ecosystems. In this study, we used stable nitrogen isotope analysis to determine the trophic position of fish in Raohe River during the dry season. Then we estimated the relationships between body length and trophic position of Pseudobagrus fulvidraco and Hemiculter bleekeri and the δ¹⁵N values of POM, respectively. Spatial variation in trophic position of fish was compared among the upper, middle, and lower areas and estuary of the Raohe River, and the main impacts of the trophic position were also analyzed. The results showed that δ¹⁵N values of fish in Raohe River ranged from 4.7‰-15.6‰, and for most of the fish species δ¹⁵N values were concentrated from 10‰ to 14‰. The values of δ¹⁵N in Hemiramphus intermedius were highest ((15.6±1.6)‰), which was collected in Lake Poyang. However, crucian carp collected in Qiaomuwan had the minimum values of δ¹⁵N ((4.7±0.9)‰). From the δ¹⁵N values of consumers, we estimated that fish occupied 3 to 4 trophic levels in Raohe River; 75% of fish species had a high trophic position of more than 3, and the trophic position of almost 10% of fish species was less than 2, which might be related to the increase in predation and starvation because of enhanced predator-prey interactions during the dry season. In addition, spatial variation in the trophic position of fish also occurred in Raohe River, reflecting that fish in Lake Poyang and its estuary had a higher trophic position than those in the upper, middle, and lower areas. That results were consistent with variation in δ¹⁵N values of POM, which were strongly affected by intensity of N input from the catchment, revealing that the trophic position of fish in Raohe River was largely affected by food sources but not by body size. Consequently, this study may add to the knowledge of the structure of the food web in Raohe River.