Objective Based on the actor-partner interdependence model, to investigate the inverse relationship between psychological capital levels and fear of recurrence of cancer in lung cancer patients and their primary family carers.Methods A cross-sectional survey design was adopted. From February to October 2025, 231 lung cancer patients and their family caregivers were selected as study participants using convenience sampling from the oncology department of a tertiary traditional Chinese medicine hospital in Shanghai. Data were collected using the general demographic questionnaire, the positive psychological capital questionnaire and the simplified scale of fear of disease progression.Results Both patients and caregivers had a medium to high level of psychological capital, with the latter scoring significantly higher. Converse, patients reported a higher fear of recurrence of cancer than caregivers. A Pearson correlation analysis showed that psychological capital was negatively correlated with FCR in both cohorts. The actor-partner interdependence model also identified important effects between actors and partners, suggesting that higher psychological capital in one individual is associated with lower FCR in both himself and his partner. The model showed a good fit (χ²-df = 4.582, CFI = 0.959, RMSE = 0.038).Conclusion Psychological capital significantly reduces the fear of cancer recurrence in lung cancer patients and their family caregivers, and has shown notable effects on partners. These findings suggest that psychological capital functions as both an individual and a shared emotional resource in the dyads of patients and caregivers. The