In this study, we developed and validated an instrument for measuring postgraduate competence and examined the relationships between postgraduate competence and academic research performance, along with the mediating role of psychological capital. Based on two independent samples, the results provided robust evidence of postgraduate competence composed of six dimensions. Adopting a two-wave survey at two different time periods, we conducted a questionnaire survey on 364 postgraduates from three top universities in China by random sampling. The results indicated that postgraduate competence was positively associated with academic research performance. Among the competences composed of six dimensions, research ability was the most predictive dimension of academic research performance. Additionally, psychological capital partially mediated the relationship between postgraduate competence and academic research performance. These findings contributed to the ongoing discussion about improving postgraduates’ academic research performance under the circumstance of competence-based education.