Using young apple fruits as raw materials, young apple powder (YAP) was prepared by vacuum freeze-drying technology, and the content of major components including polyphenols and dietary fiber was determined. A three-stage continuous fermentation system was used to simulate colonic fermentation, and combined with high-throughput 16S rRNA high-throughput sequencing and GC-MS analysis, the effects of YAP on the composition of colon microbiota and short-chain fatty acids in healthy and obese volunteers were explored. The results showed that YAP was rich in dietary fiber [(417.50±0.40) mg/g] and total polyphenolic substances [(57.10±0.03) mg/g]. YAP altered the microbiota composition in colonic reactors of healthy and obese volunteers, with no significant changes in Alpha diversity but significant differences in Beta diversity. Low-dose YAP had a significant effect on the relative abundance of different bacterial groups in the colon. YAP significantly increased the relative abundance of Bacteroidota and decreased the relative abundance of Proteobacteria in the healthy group. In the obese group, YAP significantly increased the relative abundance of Actinobacteriota. Within a 7d fermentation period, YAP had a regulatory effect on both experimental groups of genus-level colonic microbiota, resulting in their relative abundance reaching a stable value. YAP promoted the production of bacteria which could produce short-chain fatty acids and increased the total content of short-chain fatty acids in the colon of healthy and obese volunteers, with the highest content of acetic acid in short-chain fatty acids. Low-dose YAP significantly increased the concentration of valeric acid, butyric acid and caproic acid in colon samples (P<0.05). The results of simulated colonic fermentation in vitro showed that YAP rich in polyphenol-dietary fiber could significantly regulate the composition of colon microbiota and short-chain fatty acids in healthy and obese volunteers. This study aimed to provide new ideas and theoretical basis for dietary regulation of gut microbiota.