Based on the theoretical framework of the Knowledge -Attitude - Practice（KAP）theory and the Rainbow Model，this study systematically analyzes the key factors influencing the development of science popularization competencies among medical students using a dual analytical framework of“internal and external factors”. A total of 699 valid questionnaires were collected from a medical university. Linear regression models were employed to assess the association between science popularization competency（dependent variable）and the dual framework of internal and external factors（independent variables）. The Shapley value decomposition method was further used to estimate the relative contributions of each variable to model fit. The results indicate that Internal factors，including knowledge（β=2.758），attitude（β=0.950），and practice（β=0.531），significantly promote science popularization competency. Among external factors， institutional - level influences also demonstrated a significant positive effect（β=0.714）. Shapley value decomposition revealed that knowledge and attitude contributed most substantially to the science popularization competency. Knowledge，attitude，and practice serve as core driving forces of science popularization competency among medical students，while institutional factors act as critical supportive elements. Among internal factors，knowledge and attitude exhibit the highest explanatory power. The findings suggest that medical schools should prioritize both knowledge delivery and attitude guidance，while strengthening external support for health science popularization policies. This will effectively enhance the science popularization competencies of medical students and provide a solid foundation for improving public health literacy.