Abstract: 【Objective】The special phenotypic traits and correlation at different growth stages of Hippocampus abdominalis were explored,and the main morphological traits affecting the quality of H. abdominalis at two-month-old were selected,which laid reference for the morphological study and artificial breeding of H. abdominalis.【Method】Tenday-old and two-month-old artificial breeding H. abdominalis were randomly collected as the research objects.The phenotypic traits including mandibular length (X₁),maxillary length (X₂),snout length (X₃),eye diameter (X₄),head length behind the eye (X₅),head length (X₆),trunk length (X₇),tail length (X₈),dorsal fin length (X₉),body length (X₁₀) and body weight (Y) were measured.The correlation of phenotypic traits and main development direction of 10-day-old and2-month-old H. abdominalis were compared by correlation analysis and principal component analysis.The effects of main morphological traits on body weight of 2-month-old H. abdominalis were studied by path analysis and grey correlation analysis.【Result】Except for the insignificant correlation between mandibular length and dorsal fin length of 10-day-old H. abdominalis(P>0.05),the correlation coefficients of other traits at the two stages were significant (P<0.05) or extremely significant (P<0.01,the same below).The focusing directions of principal component were different at different stages.From 10-day-old to 2-month-old H. abdominalis,the initial body length increased rapidly,the growth and development of head and snout were obvious at first,and the growth of the trunk was focused in the later stage.Path analysis results of 2-month-old H. abdominalis showed that head length and body length were the main morphological traits affecting body weight.The largest direct effect on body weight was body length (0.763),while the largest indirect effect on body weight was head length through the body length (0.278).The regression equation(Y=-1.817+0.038X₆+0.029X₁₀) could accurately predict the change of body weight (F=127.556,P<0.01).The grey correlation analysis results showed that the main morphological traits with high correlation to body weight included trunk length,tail length,head length and body length,the corresponding correlation coefficients were 0.787,0.754,0.745 and 0.724 respectively.The results of different analysis methods were slightly different,but body length was found to be the main morphological traits with high correlation degree with body weight by all methods.【Conclusion】From 10-day-old to 2-month-old,the growth of H. abdominalis changes from head and snout to trunk.When using body weight as the target trait for 2-month-old H. abdominalis breeding,body length is the main selection trait,while head length,trunk length and tail length can be collaborative selection.