Fragrant citrus （Citrus × junos Siebold ex Tanaka） and Poncirus trifoliata （L.） Raf. grafted Wuming Orah mandarin were used to study the effects of different rootstocks on the quality of mature fruits and clarify the optimal harvesting period for Wuming Orah mandarin.Samples of fruit were collected at 8 developmental stages （S1-S8） spanning the color-break period to full maturity to determine the key parameters of quality including the color index of fruit pericarp，the content of total soluble solids （TSS） and titratable acidity （TA），juice yield，and changes in indexes of quality such as primary metabolite profiles at five critical stages.RNA-Seq was used to analyze differences in gene expression at three pivotal stages，and qRT-PCR was used to verify the expression of key genes.Results showed that P. trifoliata-grafted fruits exhibited accelerated pericarp coloration and enhanced redness during S1-S5.The juice yield，TSS，and TSS/TA ratio in P. trifoliata-grafted fruits increased by 0.37%-11.64%，0.73%-1.00%，and 0.32-3.41 compared to that in C. junos-grafted fruits.The results of sensory evaluation showed that the overall preference score for P. trifoliata-grafted fruits was 8.11，significantly higher than that for C. junos-grafted fruits （7.22）.The results of analyzing primary metabolome showed that the content of sucrose，D-fructose，D-glucose，and myo-inositol in P. trifoliata-grafted fruits was significantly increased.There was no significant difference in TA，TSS/TA ratio，and sensory flavor between the two rootstocks during the same period of S6-S8.Transcriptome profiling identified 1 481 differentially expressed genes，predominantly enriched in biological processes including carbohydrate metabolism，protein phosphorylation，and transcriptional regulation.The results of qRT-PCR confirmed the early upregulation of CsSUC1 （the key sucrose transporter gene） in P. trifoliata-grafted fruits.It is indicated that the optimal harvesting period for P. trifoliata grafted Wuming Orah mandarin occurs in early January，approximately two weeks earlier than that for C. junos grafted fruits （mid-January）.The main reason why P. trifoliata rootstock promotes fruit ripening is related to accelerating the accumulation of soluble sugars in the fruit of Wuming Orah mandarin.