Abstract: In order to study the relationship between morphological traits and body mass, 477 clams (Callista erycina) were randomly selected form Beihai, Guangxi Province to measure their shell length, shell height, shell width, anterior length, posterior length,  number of growth lines  and body mass by correlation analysis, path analysis and multiple stepwise regression analysis. The results show that there was extremely significant correlation among all the phenotypic traits (P<0.01), among which the correlation coefficient between shell length and anterior length was the highest (0.886), and that between posterior length and number  of growth lines was the lowest (0.180). The correlation coefficients of body mass with shell width and posterior length were the highest (0.865) and  the lowest (0.474) , respectively. We established a regression equation of morphological traits for body mass (R²=0.812). The shell width influenced the body mass most with a path coefficient of 0.665, followed by shell length (0.154) and shell height (0.117). The anterior length had the greatest indirect effect on the body mass (0.586), followed by shell height (0.580) and shell length (0.504). The shell width was the most important determinant of body mass (0.442), followed by the shell length (0.024). The results suggest that breeding of C. erycina with body mass as breeding objective should mainly select shell width, and the synergistic breeding of shell length and shell height should be strengthened at the same time.