Abstract: In order to explore the effects of morphological traits on body weight of S. intermedius at different ages.the shell diameter, shell height, diameter of the peristome, maximum width of the ambulacrum, maximum width of the interambulacrum, and body weight of S. intermedius were measured. We conducted correlation analysis to assess inter-trait relationships and employed an integrated approach combining path analysis, multiple regression, and allometric growth modeling to evaluate morphological trait effects on body weight parameters (path coefficients, determination coefficients, and correlation indices). The analysis revealed statistically significant correlations (P<0.01) among all measured traits in S. intermedius across four developmental stages (10, 16, 22, and 28 months of age). Based on the direct path coefficients of morphological traits' effects on body weight, it can be seen that shell diameter has the greatest effect on the body weight of S. intermedius at each month of age. Through the stepwise regression method,multiple regression equations for body weight (BW) and morphological traits of sea urchins at each month of age were established. The results of allometric growth analysis showed that the growth parameters of 10～28-month-old S. intermedius which were greater than 1, indicating that they were in the allometric growth stage (positive allogenesis). With the increase of the age of sea urchins, the effects of various morphological traits on body weight changed, among which the effect of shell diameter on body weight of sea urchins increased first and then decreased, and the effects of other morphological traits on body weight gradually increased with the increase of sea urchins' age at months. Therefore, shell diameter was the main selective trait in the breeding process for 10～28-month-old sea urchins, which had the greatest impact on their body weight. Other morphological traits, such as shell height and diameter of the peristome, can be used as auxiliary selective traits.