Objective: To explore the mediating role of social support in post-traumatic growth and cancer recurrence fear in breast cancer patients by using structural equation model. Methods: A cross-sectional survey was conducted in 358 patients with breast cancer, they were assessed with the self-reported questionnaire, the perceived social support scale (PSSS), the posttraumatic growth inventory-Chinese version(PTGI) and the fear of cancer recurrence inventory-Chinese version(FCRI-CV). Results: The total score of posttraumatic growth of breast cancer patients was negatively correlated with the total score of fear of cancer recurrence（ r=-0.462, P<0.01）, and positively correlated with the total score of social support（ r=0.668, P<0.01）. Structural equation model showed that social support partially mediated the relationship between fear of cancer recurrence and posttraumatic growth( GFI=0.963, AGFI=0.900, RMSEA=0.052), accounting for 60.43% of the total effect. Conclusion: Fear of cancer recurrence can not only directly predict posttraumatic growth, but also indirectly predict posttraumatic growth through social support.