This study investigated Liparis nervosa, an Orchidaceae medicinal plant, to systematically optimize its fermentation process using microbial fermentation technology and to evaluate its therapeutic potential against ulcerative colitis (UC). Based on single-factor experiments and orthogonal design, total antioxidant capacity was used as the primary evaluation index, and the optimal fermentation conditions were determined as follows: 1% aqueous extract concentration, fermentation temperature of 35 °C, and fermentation time of 4 days. Under these conditions, the antioxidant activity of the fermented product was significantly enhanced, accompanied by increased flavonoid content and hydroxyl radical scavenging capacity, while total phenolic content decreased, suggesting that fermentation promotes structural transformation and functional optimization of bioactive components. In a dextran sulfate sodium (DSS)-induced mouse model of UC, fermented Liparis nervosa extract significantly improved general physiological conditions, reduced the disease activity index (DAI), and alleviated colon shortening and tissue damage. At the molecular level, fermented Liparis nervosa downregulated pro-inflammatory cytokines, including TNF-α, IL-6, and NF-κB, while upregulating intestinal barrier-related proteins such as ZO-1, Claudin-1, and Mucin-2, thereby promoting mucosal repair. In conclusion, optimized fermentation enhances the antioxidant and anti-inflammatory activities of Liparis nervosa, enabling it to ameliorate UC through multiple mechanisms, including inflammation suppression, intestinal barrier restoration, and modulation of gut microbiota. This study provides a theoretical and experimental basis for the development of Liparis nervosa-based functional foods and traditional Chinese medicinal preparations.