In order to better understand the nutritional niche changes during the ontogeny period of Ommastrephes bartramii and Onychoteuthis borealijaponicus,36 O.bartramii and 30 O.borealijaponicus samples were collected from "Songhang" fishery resources survey ship in 2021-2022, and stable isotopic analysis was conducted on their eye crystals. The results show that： the variation in individual δ¹³C and δ¹⁵N values for O. bartramii ranged from 0.10‰ to 1.68‰ and 0.79‰ to 7.51‰, respectively； and the variation in individual δ¹³C and δ¹⁵N values for O. borealijaponicus ranged from 0.15‰ to 1.20‰ and 0.81‰ to 7.05‰, respectively. The niche area change range for O. bartramii and O. borealijaponicus was 0.40‰²-5.85‰² and 0.27‰²-5.36‰², respectively. GAM model analysis showed that the δ¹³C and δ¹⁵N values of O. bartramii eye crystals had a significant correlation with crystal diameter, with deviation interpretation rates of 31.9% and 34.3%, respectively. Similarly, the δ¹³C and δ¹⁵N values of O. borealijaponicus eye crystals were significantly correlated with crystal diameter, with deviation interpretation rates of 12.9% and 19.4%, respectively. According to the analysis,O.bartramii and O.borealijaponicus feeding flexibility is responsible for the irregular change of δ¹³C and δ¹⁵N values with increasing carcass size. The larger magnitude of individual isotopic changes reflects the greater magnitude of baseline isotopic values in the Kuroshio-Oyashio transition zone in Northwest Pacific Ocean. Additional 83% of the O.bartramii samples and 80% of the O.borealijaponicus samples niche amplitude of δ¹³C was small,but niche amplitude of δ¹⁵N was larger,so the feeding level of O.bartramii and O.borealijaponicus in this area is different. The GAM model showed that individual growth and baseline values were factors affecting the tissue δ¹³C and δ¹⁵N values.