Aims/Background The prevalence of postpartum fatigue among primipara is high in China, which seriously affects women’s subsequent physical and mental recovery. In order to deeply understand this phenomenon, domestic scholars began to conduct research on postpartum fatigue from the aspects of assessment tools and intervention measures. This study aims to investigate postpartum fatigue in primiparous women and its association with family functioning and social support, providing valuable insights for improving the condition in this population. Methods Primiparous women from February 2023 to March 2024 were selected as participants. Baseline demographic information was collected, and postpartum fatigue levels were assessed using Postpartum Fatigue Scale (PFS) at 7 days postpartum. Social support was evaluated with Postpartum Social Support Scale, and maternal role adaptation was assessed using Maternal Role Adaptation Questionnaire (MRAQ). Pearson correlation analysis was conducted to examine the relationship between postpartum fatigue levels, role adaptation, and social support. Results A total of 210 survey questionnaires were distributed; following which, 201 valid questionnaires were received. The total PFS score was 13.93 ± 4.53 points. Among the participants, 50 cases (24.87%) experienced no fatigue, 58 cases (28.86%) with mild fatigue, 78 cases (38.81%) with moderate fatigue, and 15 cases (7.46%) with severe fatigue. There were statistically significant differences in all dimensions and total scores of the Postpartum Social Support Level Scale for primiparas with different levels of postpartum fatigue (p < 0.001), with those facing severe fatigue reporting significantly lower level of social support. There were statistically significant differences in the comparison of each dimension and total score of the role adaptation scale for primiparas with different levels of postpartum fatigue (p < 0.001). The degree of role adaptation in patients with severe fatigue was significantly lower. The PFS score of primiparas was negatively correlated with the level of social support and role adaptation (r = –0.693, r = –0.735, p < 0.001). Conclusion The majority of primiparous women experience varying degrees of postpartum fatigue at 7 days postpartum. Poor newborn health, artificial feeding, and nighttime feeding frequency ≥4 times per night can exacerbate postpartum fatigue. Good social support and role adaptation are beneficial in alleviating postpartum fatigue. Strengthening social support and role adaptation can help reduce postpartum fatigue levels in primiparous women.