Abstract: Changes in physicochemical quality, nutrient composition and volatile substances of juice from Orah mandarin harvested at different maturity levels were investigated. The results showed that with the extension of the harvest period, the L^* value of Orah mandarin juice decreased, and the range of a^* value and b^* value was −0.22~1.87 and 13.57~15.30, respectively. The color of Orah mandarin juice at harvest period Ⅴ and Ⅵ was better. The content of soluble solids, solid-acid ratio of Orah mandarin juice increased first and then decreased, while the change of titratable acid content was unstable, and the solid-acid ratio of Orah mandarin in Ⅴ and Ⅵ harvest periods was suitable. The amino acid content of Orah mandarin juice increased first and then decreased, and the content of vitamin C and carotenoid increased gradually, while the content of total phenols and limonin showed a downward trend. According to the cluster analysis, the content of nutritious components of Orah mandarin in the harvest period of IV and V were higher. In addition, it was found that the electronic nose could accurately identify the characteristic odors of Orah mandarin juice with different maturity levels. The results showed that sensor W1W had the largest contribution rate of principal components, followed by sensor W2W. A total of 38 main aroma compounds were identified in Orah mandarin juice with different harvest maturity. Olefins were the most important aroma substances, among which D-limonene had the highest relative content, and its relative contents in Orah mandarin juice with different harvest maturity were 83.71%, 60.31%, 75.87%, 83.25%, 81.85%, 80.1%, 91.52%, respectively. Alcohols, esters, aldehydes, and ketones showed a dynamic change rule of first increasing and then decreasing at different fruit harvesting periods, while the overall changes of hydrocarbons were the opposite. The relative contents of these five substances in Orah mandarin juice at harvest periods Ⅳ, V and Ⅵ were all higher. Based on the above, the juice quality of Orah mandarin at harvest period V was relatively best.