Abstract: The aim of this experiment was to study the fruit development and main quality indexes’formation of nectarine under protected cultivation in southern Xinjiang arid areas. With‘Zhongyoutao No.5’as the experimental material, the author tested and analyzed external and internal fruit quality indexes by periodical sampling during fruit development. The research results demonstrated that in the protected cultivation, the fruit growth curve of‘Zhongyoutao No.5’was double‘S’shape and in accordance with stone fruits. The internal fruit quality indexes such as titratable acid, soluble sugar, sucrose, vitamin C and soluble solids accumulated rapidly or changed before close to maturity, the fruit flavour was improved because of sugar- acid ratio gradually increased. The key period of fruit development and quality formation was 15 days before fruit maturation. In order to improve fruit quality, it is important to emphasize nutrition supply and fertilizer regulating in the later stage of fruit growth.