【Objective】The purpose of this study is to understand the changes in sugar and other quality indexes during fruit development, to explore the potential mechanism of carbohydrate accumulation during blueberry (Vaccinium spp.) fruit development, and to establish a theoretical foundation for blueberry quality enhancement.【Method】Fruits of six blueberry cultivars at different developmental stages were used as the test materials. The morphological traits (size and color), antioxidant system-related parameters, fruit quality indexes, the expression levels of VcSWEETs genes, and sugar composition and content were determined. The correlation analysis among these parameters was performed using the Pearson correlation model.【Result】With the development of the fruit, the fruits of each cultivar gradually increased in size and deepened in color, of which the ‘Legacy’ cultivar had the largest fruit weight and transverse diameter, and ‘Zhongzhi 2’ had the smallest during the purple fruit stage (S3). In the S3 period, ‘Legacy’ showed peak L value with minimal a^* and b^* values. The generation rate of O_2^{\stackrel{-}{\underset{·}{ }}} and MDA content steadily increased, while H₂O₂ content (excluding ‘Zhongzhi 4’) and SOD activity decreased first and then increased, and POD activity gradually increased. Total soluble solids (TSS) and anthocyanin contents gradually increased, flavonoid content gradually decreased, and ellagic acid content initially decreased and then increased. Among them, ‘Zhongzhi 4’ had the highest TSS and anthocyanin content during the S3 period. The expression patterns of three VcSWEETs genes exhibited distinct cultivar specificity and developmental stage dependence. Sucrose, glucose, fructose, and total sugar accumulated continuously, though glucose maintained basal levels. In the S3 period, the total sugar contents of all cultivars were more than 200 mg/g, except for ‘Zhongzhi 1’.【Conclusion】Sugar content increased continually during fruit development, with sucrose and fructose concentrations predominating over glucose. ‘Legacy’ had the greatest total sugar content during the S3 period, followed by ‘Zhongzhi 2’ and ‘Zhongzhi 4’. The expansion of the fruit, the rise in anthocyanin content and POD activity, and the up-regulated expression of the VcSWEET1 gene were significantly correlated with sugar accumulation patterns.