The shaded fruits in the inner canopy of Orah mandarin and the fruits with sufficient light at the periphery of the canopy were used to compare and analyze the comprehensive effects of light conditions on the appearance,color and internal quality of Orah mandarin. The results showed that the shaded fruits presented a deeper orangered color compared with the fruits with sufficient light. The content of total carotenoid in the peel of the shaded fruits increased by 2.87 times,and the main color pigments β-citraurin (red) and 9-cis-violaxanthin (orange yellow) were increased by 16.93 times and 6.47 times,respectively. The results of gene expression analysis showed that the main structural genes of carotenoid metabolic pathway were significantly up-regulated in shaded fruits. The expression of carotenoid cleavage dioxygenase (CCD4b),a key gene for β-citraurin biosynthesis,increased by 11.78 times. It is indicated that shading can promote carotenoid accumulation in the peel of Orah mandarin by inducing the expression of genes related to carotenoid biosynthesis,and ultimately make the peel dark orange-red. The content of soluble solids,titratable acid,soluble sugar,organic acid and ascorbic acid in shaded fruit was much lower than that in the fruit with sufficient light,indicating that light conditions affected the internal quality of the fruit. It will provide a theoretical basis for further elucidating the underlying mechanisms of how light regulate fruit quality,and ultimately improving the fruit quality of citrus by breeding and cultivation.