Psychological factors may play an important role in interpreting performance and its development during training; meanwhile, the development of interpreting competence may influence psychological factors reactively. We conducted two studies to assess the bidirectional relationship between three psychological factors (self-efficacy, motivation, and anxiety) and interpreting performance in interpreting students. Study 1 was a longitudinal study, assessing 51 undergraduate students of interpreting twice, at the beginning (Time 1) and end (Time 2) of their first training year. Study 2 collected data from 40 Master's students of interpreting to enable a cross-sectional comparison with Study 1. The correlation analyses and hierarchical regression analyses showed that in Study 1, learning motivation and self-efficacy decreased whereas anxiety remained relatively stable; interpreting-specific anxiety was negatively correlated with concurrent interpreting performance at both times; motivation at Time 1 significantly contributed to the development of interpreting competence. When the two studies were compared, Master's students had higher learning motivation and self-efficacy but lower anxiety than undergraduate students (at both times). The findings illustrated the differential development of psychological factors and their relations to interpreting competence. The results have implications for research in interpreting competence and interpreting training.