The central western South China Sea is one of the main fishing grounds for fishery development. To understand the trophic relationships of major fishery organisms of the central western South China Sea, stable isotope techniques were used to analyze and determine carbon and nitrogen stable isotope ratios of major fishery biological samples in the area. The trophic levels of the main fishery biota were calculated to construct a continuous trophic spectrum of the main fishery organisms in the area. These results show that the major fishery isotope ratios have a wide range of changes in the central western South China Sea. The δ¹³C and δ¹⁵N values of the fish ranged from -20.00‰ to -16.51‰ and from 7.94‰ to 11.81‰, respectively. The δ¹³C and δ¹⁵N values of the cephalopods ranged from -18.84‰ to -17.60‰ and from 10.10‰ to 12.85‰, respectively. The corresponding trophic levels of each species were calculated using zooplankton as the baseline organism. The trophic level of fish ranged from 2.41 to 3.53, and that of cephalopods ranged from 3.03 to 3.84. Among the organisms, the average trophic level of cephalopods is higher than that of fish. Comparison of trophic levels in different lengths (mantle length) of Symplectoteuthis oualaniensis, Thysanoteuthis rhombus, Decapterus russelli, Decapterus lajang, and Thunnus albacares reveals that the trophic level has a correspondingly increasing trend as body length increases. In this study, we preliminarily established the continuous trophic levels’ spectrum of major fishery bio-nutritional levels in the central and western waters of the central western South China Sea, providing a theoretical basis for the food web structure and fishery resource utilization in the area.