Abstract: Acacia mearnsii seedling at the nursery of Guangxi forestry research institute was selected as material to study the height and ground diameter growth of seedlings in different month, analyzed their growth rhythm, and then fit the growth process of semiannual seedling by using Logistic curve and S curve. The result showed that the growth process of semiannual seedling had obvious intermittently. There were two peaks of both height and basal diameter in semiannual seedling, and the time of occurrence was consistent. Logistic curve was more appropriate to describe the growth of height and basal diameter than S curve. The seedling growth could be well predicted by fitting curves, and then provided direct decisions for nursery seedling and forestation. According to aboveground part growth characteristics of the semiannual seedling, seedling growth could be dividing into three stages: early growth period, fast growth period and later growth period. Therefore, different cultivate seedlings measures should be adopted according to the characteristics of different growth stages.