In order to analyze the relationship between morphological traits and body weight of grass carp at different month ages, we measured morphometric traits at 2-month-old stage,4-month-old stage,6-month-old stage,and 12-month-old stage, respectively, in this study. The correlation analysis, path analysis and multiple regression were used to calculate correlation coefficient, path coefficient and the coefficient of determination between morphological traits and body weight. Correlation analysis showed that morphological traits and body weight of each month-old grass carp were significantly correlated (P<0.01). Path analysis showed that at 2-month-old stage and 6-month-old stage,the trait with strongest direct effect on body weight was the body height,but at 4-month-old stage,12-month-old stage, the trait with strongest direct effect on body weight was the body length, and at every stage the trait with strongest indirect effect on body weight was body width. The result of determinant coefficient analysis was consistent with that of path analysis. Partial regression coefficient significance test three morphological traits are highly significant, and at each stage the multiple regression equation relating the body weight can be established. Studies have shown that at 4-month-old stage and 12-month-old stage adjusted coefficient of determination is greater than 0.85, the major morphometric traits affecting body weight of grass carp at different growth stages have been identified. This study provided the basic data for grass carp at different growth stages of breeding.