Objective. This study aims to construct a comprehensive model that can explain and predict Chinese college students' intentions to engage in physical activity based on Self-Determination Theory (SDT) and the Theory of Planned Behavior (TPB). Methods. This study selected four colleges from Chengdu, China for random sampling, with a total of 512 college students completing the questionnaire. Structural equation modelling (SEM) was used to examine the research hypotheses. Result. Psychological need, which includes autonomy, relatedness and competence facilitates intrinsic motivation to to exercise among students. Furthermore, psychological need and intrinsic motivation also play important role in influencing student attitude and behaviour on physical activities. Conclusions. Students who experience greater autonomy in choosing their workouts, competence in their abilities, and relatedness through peer support are more likely to develop long-term exercise habits. This study contributes theoretically by extending TPB with SDT components, providing a more comprehensive understanding of exercise motivation. It offers insights for universities, fitness professionals, and health organizations to design interventions that foster motivation, social engagement, and accessibility in exercise programs.