Urban vibrancy can facilitate human activities and social interactions, attract capital and talent, enhance competitiveness and creativity, maintain resilience, and finally achieve a sustainable urban development. Theoretically, transit-oriented development (TOD) is beneficial for vibrancy. In practice, TOD implementation does not always lead to vibrant community life. To foster vibrancy around stations, we need to understand relationships between TOD-ness (i.e., the degree to which the current (physical) conditions of station areas meet the standards of TOD) and vibrancy. Empirical studies on this topic are scarce, despite numerous studies on built environment effects on vibrancy. Moreover, these studies are likely to overestimate/underestimate the effects as most of them neglect the pervasive nonlinearity and synergism. This research contributes to the understanding of nonlinear and synergistic effects of TOD on vibrancy by constructing gradient boosting decision tree model using multi-source data from 166 metro station areas in Shenzhen, China. Local explanations for the model indicate the following: (1) Sufficient bus services, horizontal built-up coverage, and mixed-use buildings are dominant contributors to vibrancy around metro stations. (2) TOD have nonlinear influences on vibrancy. (3) Synergistic effects are evident among/within TOD dimensions. Practical implications of the findings, such as targeted policies with nuanced planning/design criteria, are further discussed.