Lactiplantibacillus plantarum can activate aryl hydrocarbon receptor (AHR) signaling in the gut by metabolizing tryptophan, thereby counteracting inflammation. However, the tryptophan metabolic characteristics of microorganisms are strain-specific and significantly influence their AHR-activating effects. In this study, four strains with different tryptophan metabolic profiles were screened, and a dextran sulfate sodium-induced colitis model was established in C57BL/6 mice. The key tryptophan metabolic characteristics of L. plantarum involved in AHR downstream signaling activation to alleviate colitis were explored. The results showed that strain SFFI50, characterized by poor tryptophan metabolism, and strain SFFI175, which produced high levels of IAA and ICA, did not alleviate colitis. Strain SFFI118, capable of metabolizing tryptophan to produce IAA, ICA, and ILA, could slightly restore mouse body weight, DAI, and IL-22 expression. L. plantarum SFFI23 significantly restored body weight, colon length, histopathological damage, and cytokine expression in mice. Moreover, it activated the downstream signaling of AHR, specifically CYP1A1, and repairs the intestinal barrier function. Targeted metabolomic analysis revealed a significant increase in indole-3-lactic acid (ILA) in the mouse intestine. Correlation analysis revealed a significant positive correlation between high ILA production of L. plantarum, CYP1A1 expression, intestinal barrier function restoration, ILA levels in vivo, and colitis alleviation. Therefore, we inferred that high ILA production is a key tryptophan metabolic characteristic of L. plantarum which activated AHR downstream signaling (such as CYP1A1, IL-22, and STAT3) to alleviate colitis. This study provides a theoretical basis for the development of personalized dietary interventions to improve gut health.