In order to research on the rule of the relative growth of traits of Litopenaeus vannamei and judging the age matching with the size of L. vannamei missing the best growing season, the data acquired by measuring the total length(X1), body length(X2), first abdominal segment depth(X3), third abdominal segment depth(X4), first abdominal segment width(X5), carapace length(X6) and body weight(Y) of Penaeus vannamei at different ages in Banqiao Village of Dongfang City, Hanan Province were analyzed by principal component and discriminant analysis. Result shows that the correlation between any two traits of L. vannamei is significant（P<0.01）at all tested ages., among which those between the total length(X1) and body length(X2) are relatively larger and those between body weight(Y) and morphometric attributes are relatively smaller. The principal components of L. vannamei at different ages are different. For example, the first principal component of L. vannamei at from one month of age to two months is length factor, the second principal component is width factor and the third principal component is depth factor. Also, for L. vannamei at three months of age, its first principal component is the same as that at from one month of age to two months, but its second principal component is depth factor and its third principal component is body weight factor. Finally, the first principal component of L. vannamei at from four months of age to six months is body weight factor, the second principal component is depth factor and the third principal component is width factor. The results of principal component analysis reflect that the growth of morphometric attributes of L. vannamei at from one month of age to three months takes priority compared with that of body weight, but the growth of body weight of L. vannamei at from three months of age to six months is given priority to compared with that of morphometric attributes. The month age closely related to the size of L. vannamei which has missed the best growing period can be deduced by employing the discriminant equations mentioned in this paper and the results of the discriminant analysis demonstrate that the overall accuracy is 98.98% and those of L. vannamei at two months of age to four months all reach 100%.