Background <p>Research ability is a key indicator for assessing the quality of training and academic competitiveness among postgraduate students in medical academic programs. Psychological capital, as an important positive psychological resource, has not yet been systematically investigated in terms of its influence mechanism on research ability within the context of medical postgraduate education.</p> Methods <p>This study employed convenience sampling. Between June and July 2023, an online questionnaire survey was conducted among 3,892 medical academic master’s students from 70 Chinese universities through the Sojump online platform. Hierarchical regression and moderated mediation analyses were performed via SPSS 27.0 and the PROCESS macro (version 4.1).</p> Results <p>Psychological capital not only significantly and positively predicts the research ability of medical academic master’s students but also has an indirect effect via research investment. Moreover, mentorship guidance plays a dual moderating role in this mediation process: it strengthens the impact of psychological capital on research investment (<i>β</i> = 0.031, <i>P</i> &lt; 0.05) and increases the efficiency of converting research investment into research ability (<i>β</i> = 0.053, <i>P</i> &lt; 0.01).</p> Conclusions <p>Psychological Capital and Mentorship Guidance play a crucial role in enhancing Research Investment and Research Ability among Master of Medical Studies students. This empirical study enriches the evidence base on the mechanisms through which positive psychological resources promote research competence, provides a foundation for strengthening graduate medical education through policies centered on Psychological Capital and Mentorship Guidance, and offers both theoretical insights and practical implications for optimizing the cultivation model of scientific research talent.</p>