Abstract: In this study, we selected 5-month-old yellow fin tuna (Thunnus albacore) juveniles as the experimental objects to explore the correlation between the 14 morphological traits and body mass. The results show that there was a very significant positive correlation between them (P<0.01), and the direct effect of pectoral fin length on body mass was found by path analysis (0.507), followed by full length, and upper jaw length mainly affected body mass indirectly through full length, head length and pectoral fin length. The determination coefficient analysis shows that the total decision coefficient of four morphological traits was 0.954, which further indicates that body mass was mainly affected by the above traits. Through multiple regression analysis, the regression equation of morphological traits to body mass was established, and the optimal fitting curve model was selected. In the actual production, the length of pectoral fin should be taken as the main morphological trait reference in breeding 5-month-old yellowfin tuna, and full length, head length and maxilla length as the auxiliary traits reference.