Based on the fishery biological survey data of the southwestern continental shelf of the Nansha Islands area in spring 2023, the trophic positions of major fishery organisms and the overlap of trophic niche among different functional groups were investigated by applying the carbon and nitrogen stable isotope techniques, and trophic continuum profiles were constructed. The results showed that the δ¹³C values of the fishery organisms ranged from −20.31‰ to −17.56‰, with a mean value of (−19.07±0.72)‰, δ¹⁵N values ranged from 7.79‰ to 10.80‰, with a mean value of (9.28±0.77)‰. Using zooplankton as the baseline organism, the trophic level of the fishery organisms ranged from 2.95 to 4.29. Compared with other marine areas in the South China Sea, the food chain length of the main fishery organisms in the southwestern continental shelf of the Nansha Islands area was relatively short, the initial food source was relatively single, the width of the niche was small, the degree of redundancy of consumers in the food web was high, and competition for food among species was intense. The results of cluster analysis of δ¹³C and δ¹⁵N values of fishery organisms were classified into four trophic groups, namely, zooplankton feeding group, mixed feeding group, large predator feeding group, and benthic feeding group, and the differences among the trophic groups were significant (P＜0.01). The trophic niches of fishery organisms were analyzed according to the δ−space (95% confidence interval) standard ellipse and structural parameter indexes, and it was found that the SEAc=0.66‰² . NR (δ¹⁵N range) and CR (δ¹³C range) of the mixed feeding group were 1.93 and 1.64, respectively, which indicated that the food resources were widely utilized and the food chain was long in this community. The niche overlap rates of the mixed-feeding group with plankton, large carnivores, and benthic feeding groups were 7.32%, 5.42%, and 0.60%, respectively. Compared to the pelagic zone in the central and western parts of the South China Sea, the overlap rate of trophic groups on the southwest shelf of Nansha was relatively low, indicating that the trophic niches of fishery organisms in different layers of the South China Sea have distinct spatial differentiation characteristics.