The fruits of Qiongdong No. 9 Camellia oleifera at five developmental stages were taken as the experimental materials to ascertain the basic characteristics of the growth and development in Hainan and the changes in the content of antioxidant active substances. The morphological characteristics were observed, the crude fat and six main active ingredient contents of the seeds at different developmental stages were measured, and four antioxidant activity indicators of the seeds at different developmental stages were detected. The results demonstrated that the growth changes of each part of the fruit generally followed a logistic curve, presenting a slow increase in the initial stage, a rapid growth in the middle stage, and eventual stabilization. During the whole growth period, changes in crude fat content continued to accumulate, with S₃-S₅ being the period of rapid oil accumulation; the changing trends of the contents of flavonoids, total polysaccharides, vitamin E, ABTS radical scavenging ability and total antioxidant activity (FRAP) in seed kernels were consistent, experiencing a process of rapid decrease-significant increase-slow decrease. The content of carotenoids and the ability to scavenge hydroxyl radicals showed a significant increasing trend at all stages. The content of total phenols, total saponins, and total antioxidant activity (DPPH) showed a gradually decreasing trend. Through Pearson correlation analysis, the content of six active ingredients was significantly correlated with four antioxidant capacity indicators to varying degrees, and each ingredient had a different degree of response to different antioxidant capacities. S₁–S₃ were the rapid swelling stages of the fruit, accompanied by significant fluctuations in the content of active ingredients. S₃–S₄ were the key stages of substance transformation, and S₄–S₅ were the steady-state accumulation stages of contents; In the early stages of fruit development (S₁–S₃), water-soluble antioxidant components such as phenols, saponins, and polysaccharides dominated, while in the middle and late stages (S₃–S₅), they shifted towards lipid soluble components (carotenoids) and lipids. This competitive process was an important reason for the decrease in the content of the main active components. This research revealed the growth and development characteristics of C. oleifera fruits in tropical areas, which would have theoretical reference value for formulating corresponding cultivation and management measures for quality breeding purposes.