Abstract: Based on the potential of probiotic fermentation to enhance efficacy and improve flavor in medicinal and edible resources, sword beans (Canavalia gladiata) were selected as the raw material in this study. The processing conditions for preparing fermented sword bean milk through Lactobacillus plantarum P9 fermentation were investigated, with systematic evaluation of the bioactive components, flavor characteristics, and short-term storage stability of the fermented product. Single-factor experiments were initially performed to identify key influencing factors, followed by an L₉(3⁴) orthogonal design to optimize the fermentation parameters. Chemical assays were conducted to compare variations in bioactive constituent contents and antioxidant capacity before and after fermentation. Microstructural changes were characterized using scanning electron microscopy (SEM). Flavor evolution during fermentation and short-term storage was comprehensively profiled by electronic tongue and headspace-gas chromatography (HS-GC). Meanwhile, microbial and physical stability throughout short-term storage was evaluated in terms of pH, viable cell count, water-holding capacity, and viscosity.The findings indicated that the optimal fermentation conditions were an inoculum size of 1%, an incubation temperature of 37 ℃, and a fermentation duration of 48 h. Under these fermentation conditions, the contents of total phenols and flavonoids as well as the antioxidant activity were significantly enhanced (P<0.05). The microstructure of sword bean milk transformed from a dense structure to a loose porous network. Following fermentation, the sourness and astringency responses of the sword bean milk were significantly enhanced, leading to a distinct remodeling of its taste profile. A total of 31 volatile compounds were identified during fermentation; acids functioned as the primary flavor contributors, and together with characteristic pyrazines, formed a well-balanced flavor system dominated by acidity and complemented by nutty notes. Moreover, the fermented product maintained favorable flavor stability during short-term storage, with viable cell counts remaining above 10⁸ CFU/g. Elevated water-holding capacity and viscosity were also observed, demonstrating excellent physical and microbial stability of the final product. This study not only demonstrated the flavor enhancement and functional improvement effects of Lactiplantibacillus plantarum P9 fermentation on sword bean milk, but also provided a theoretical foundation and technical support for the development and utilization of functional sword bean products.