Objective To investigate the level of psychological capital, perceived stress and fear of cancer recurrence in breast cancer patients, and to explore the mechanism of psychological capital on the relationship between perceived stress and fear of cancer recurrence, so as to provide reference for promoting the mental health of breast cancer patients. Methods A total of 271 breast cancer patients were investigated utilizing the general information questionnaire, Positive Psychological Capital Questionnaire (PPQ), Chinese Perceived Stress Scale (CPSS) and Fear of Progression Questionnaire-short form (FoPQ-SF). Results The total score of PPQ among the patients was （110.40±19.48）. the total score of CPSS was （42.49±8.22）, and the total score of FoPQ-SF was （30.72±8.30）. Perceived stress and fear of cancer recurrence were negatively correlated with psychological capital, while perceived stress was positively correlated with fear of cancer recurrence （P＜0.01 for all）. The mediating effect of psychological capital on the relationship between perceived stress and fear of cancer recurrence was 0.101, which took account 15.51% of the gross effect. Conclusion The perceived stress among breast cancer patients is high, while their psychological capital and fear of cancer recurrence are in medium level, and patients′ perceived stress influences their fear of cancer recurrence through psychological capital. Medical staff should assess psychological capital of breast cancer patients, so as to take measures to reduce their psychological stress and thereby alleviate their fear of cancer recurrence.