Objective  To explore the relationship between occupational stress and job performance and the intermediary role of psychological capital in the relation between the two factors among medical staff in private hospitals.

  Methods  We conducted a cross-sectional survey among 824 medical staff selected with cluster sampling in 37 private hospitals in Liaoning and Hebei province and in Inner Mongolia Autonomous Region between September and December 2016. The participants were asked to complete a self-designed questionnaire, Effort-Reward Imbalance Scale, Psychological Capital Scale, and Job Performance Scale anonymously. We used Epi Data 3.1 in data processing and SPSS 22.0 and AMOS 22.0 in data analysis.

  Results  There was a significant reverse correlation between occupational stress and job performance (β = – 0.449, P < 0.001) and a significant positive correlation between psychological capital and job performance (β = 0.600, P < 0.001). Occupational stress, through psychological capital, indirectly affects job performance, with an effect size of – 0.269.

  Conclusion  Psychological capital plays a general intermediary role between occupational stress and job performance and the job performance is entirely dependent on psychological capital among medical staff in private hospitals.