This study aimed to investigate the effects of pineapple pomace as a functional feed additive on growth performance, fecal microbiota composition, short-chain fatty acids (SCFAs), and odor substance emissions in weaned piglets. The experiment utilized 90 weaned three-way crossbred piglets (Duroc–Yorkshire–Guoshou Black Pig) at 28 days of age, randomly divided into three groups of 10 pigs each: the control group (CON, basal diet), the fish meal group (FM, basal diet + 2% imported fish meal), and the pineapple pomace group (PPC, basal diet + 2% pineapple pomace compound). The results indicated the PPC group exhibited significantly higher average daily gain (ADG) (p < 0.05) and significantly lower feed conversion ratio (FCR) (p < 0.05) than the CON group. 16S rRNA sequencing analysis revealed that the PPC group significantly increased fecal microbiota species richness and diversity (p < 0.01) while enriching beneficial bacteria including Lactobacillus, Bifidobacterium, and butyrate-producing bacteria such as Blautia. Concurrently, acetic acid and butyric acid levels in feces were significantly elevated in the PPC group (p < 0.05), with butyric acid production markedly higher than in the FM group (p < 0.05). However, no significant differences were observed in the levels of branched-chain fatty acids (BCFAs), such as isobutyric acid and isovaleric acid (p < 0.05). Moreover, PPC supplementation led to a significant decrease in fecal levels of indole and 3-methylindole (skatole) (p < 0.05). In summary, dietary inclusion of 2% pineapple pomace improves growth performance and intestinal health in weaned piglets by modulating the fecal microbiota, promoting beneficial SCFA production, and inhibiting protein putrefaction. These findings support PPC as an effective and sustainable alternative to fish meal, contributing to the development of environmentally friendly feeding strategies in pig production.