The complexity and long-term nature of graduate training call for mentors to adopt diversified guidance strategies to meet the diversified demands of graduates. Authoritarian-benevolent is regarded as a wise and effective ambidextrous attitude and method in traditional Chinese family education. However, the existing studies have ignored the internal mechanism and boundary conditions of the different combinations of "authoritarian" and "benevolent" on the research ability of postgraduates. Based on the social information processing theory, this study introduces the internal and external dual approach to explore how the combination of "authoritarian" and "benevolent" affects the research ability of postgraduates. Polynomial regression and response surface analysis were used to analyze the data collected from 974 multi-time data points, and the results showed that: (1) In the consistent match, postgraduate research ability is higher in the "high authoritarian -- high benevolent" mentor than in the "low authoritarian -- low benevolent" mentor. (2) In the inconsistent match, postgraduate research ability is higher in the "low authoritarian--high benevolent" mentor than in the "high authoritarian--low benevolent" mentor. (3) The influence of authoritarian-benevolent mentor on postgraduate research ability can be mediated by research role model learning and research self-efficacy; (4) Academic atmosphere positively moderates the relationship between authoritarian-benevolent mentor and research self-efficacy and research role model learning. Our findings refine the scholarly understanding of the effects of the role of the authoritarian-benevolent mentor and provide practical insights into how mentors can effectively demonstrate a mentoring style.