This study used a sample of 818 postgraduate students across several universities in China, to explore the effect of the supervisor–student relationship on procrastination in postgraduates, and the mediating roles played by the postgraduates’ academic self-efficacy and learning adaptation. The study employs multiple scales and finds that: (1) the relationship between postgraduates and their supervisors is significantly and negatively correlated with academic procrastination; (2) the academic self-efficacy of postgraduates plays an independent intermediary role in the connection between the supervisor–student relationship and academic procrastination; (3) the learning adaptation of postgraduates also plays an independent intermediary role in the connection between the supervisor–student relationship and academic procrastination; (4) the academic self-efficacy and learning adaptation of postgraduates shows a chain-mediating effect in the connection between the supervisor–student relationship and academic procrastination. Ultimately, the supervisor–student relationship is an important factor that can directly affect academic procrastination, even if postgraduate students display academic self-efficacy and learning adaptation.