The population biology of the limpet Cellana grata in the Nanji Islands region was studied to facilitate its protection. In 2021, monthly collections of C. grata (2,624 individuals) were taken from the Nanji Islands in Zhejiang Province, China. Hierarchical cluster, regression, and path analysis were used to analyze the group composition and growth. The results showed that (1) the meat:shell ratio was highest in May, lowest in October, and the breeding season was in June. (2) The population was divided into three age groups (0–12, 13–24, and >24 mo), accounting for 33.77%, 57.96%, and 8.27% of the total population, respectively. The shell lengths were less than 25 mm (first age group), 26–34 mm (second group), and greater than 34 mm (third group), and a supplementary population (shell length 22 mm) appeared in June. (3) Growth rates were high from March to May (absolute shell growth rate:1.24, 1.45, and 0.85 mm) and September to October (0.88, 1.43 mm), and low from June to July (0.46, 0.65 mm) and November to December (0.73, 0.36 mm). Growth rates were moderate in other months (0.72, 0.74 mm). (4) The optimal regression equation between total mass (Y ) and morphological parameters (sample shell length, X ₁; shell width, X ₂; shell height, X ₃) was Y = –8.325 + 0.174X ₁ + 0.218X ₂ + 0.219X ₃ (R ² = 0.853). The effects of morphological traits on body weight were also analyzed.