Objective:To investigate the longitudinal trajectory and influencing factors of cancer-related fatigue (CRF) in breast cancer patients during chemotherapy.Methods:From March 2019 to January 2020, breast cancer patients in Longhua Hospital Affiliated to Shanghai University of Traditional Chinese Medicine, Yueyang Hospital of Integrated Traditional Chinese and Western Medicine Affiliated to Shanghai University of Traditional Chinese Medicine and Peking Union Medical College Hospital were selected as the research objects to conduct follow-up investigation. The survey tools included general information questionnaire, Cancer-related Fatigue Assessment Scale, International Physical Activity Questionnaire, and the Pittsburgh Sleep Quality Index Scale.Results:A total of 91 patients were included in the study. The incidence of severe CRF at each time point before chemotherapy, 3 weeks after chemotherapy and 6 weeks after chemotherapy were 1.1% (1/91), 8.8% (5/57) and 2.1% (1/48), respectively. The results of the generalized estimation equation showed that the trajectory of the total score CRF firstly increased and then decreased, reaching a peak at 3 weeks after chemotherapy (35.45±13.07), and mild CRF change showed statistical difference ( P<0.05). In addition, BMI and sleep and daytime dysfunction were the influencing factors of the total score of CRF. Disease stage, sleep disturbance and daytime dysfunction were the influencing factors of CRF with different severity. Conclusions:CRF is a prominent problem in breast cancer patients during chemotherapy. Attention should be paid to high-risk individuals with abnormal BMI and daytime function by medical staff.