Based on 71 Dysomma anguillare samples collected in the offshore waters of southern Zhejiang in 2016 and 2020, the trophic niche indexes were calculated by carbon and nitrogen stable isotope ratio. The trophic niche in different development processes, seasons and years were compared to explore the variation pattern of trophic niche and the utilization of resources. The results showed that:(1) the average δ¹³C values of D. anguillare in 2016 and 2020 were (-15.19±0.31)‰ and (-15.90±0.45)‰, respectively; The average δ¹⁵N values were (12.42±0.45)‰ and (12.92±0.25)‰, respectively; The results of one-way ANOVA showed that there was no significant difference in δ¹³C value (P>0.05) and δ¹⁵N value (P<0.05) at different development processes of D. anguillare in 2016. There were significant differences in δ¹³C value and δ¹⁵N value between different seasons (P<0.05); In 2020, there was no significant difference in δ¹³C value and δ¹⁵N value at different development processes of D. anguillare (P>0.05), there was significant difference in δ¹³C value between different seasons (P<0.05), and there was no significant difference in δ¹⁵N value (P>0.05). (2) From the perspective of ontogeny, the D. anguillare had a tendency to feed on highly trophic level prey food in 2016, while the feeding specialization of D. anguillare was not obvious in 2020, but the niche width decreased gradually with ontogeny, indicating that there would be interspecific resource competition and differentiation in the ontogeny stage. (3) The results of population trophic diversity index showed that the food sources of D. anguillare in autumn and winter were more extensive than those in spring and summer. The degree of trophic diversity in spring was similar to that in autumn, and that in summer was similar to that in winter. The overlap of trophic niche among seasons was small, and there was an obvious phenomenon of time differentiation. (4) Compared with 2016, the diversity index of trophic structure of D. anguillare population in 2020 decreased to varying degrees, and there was no overlap in corrected standard ellipse area (SEAc) in the two years. Due to the pressure of intraspecific and interspecific competition, it was found that there was a phenomenon of nutritional niche differentiation in the process of ontogeny and different time periods, so as to maintain species coexistence and maintain the stability of food web structure. Exploring the adaptive ability of species to the utilization of bait resources and the ecological environment has scientific significance for investigating the structural pattern and stability mechanism of marine food web.