Objective Using biological impedance analysis to monitor the body composition through the peri - radiation period. Exploring the relationship between the changes in body composition and its relationship with myelosuppression. Method A total of 60 patients with head and neck tumors in our hospital were selected from September 2022 to March 2023. The patients were collected biochemical indicators and body composition before radiotherapy 2 weeks of radiotherapy 4 weeks of radiotherapy. According to myelosuppression occurs we compared the difference in body composition of the two groups with the radiotherapy time. Computing the risk ratio of PA phase angle with myelosuppression. Comparing patients' white blood cells neutral granulocytes platelets and hemoglobin changes in low PA group and normal PA group with radiotherapy time. Result All patients' body composition have significantly decreased during radiotherapy P<0. 05 . For the myelosuppression group the contents of fat mass and visceral fat area were higher than the normal group P<0. 05 and other related indicators were lower P<0. 05 . Compared with normal PA group hemoglobin and white blood cells were lower than the normal PA group P<0. 05 and the risk of myelosuppression in low PA group is higher OR= 3. 75 95%CI = 1. 27-9. 83 . Conclusion With the progress of radiotherapy the body composition of each human will be attenuated. However the body composition measurement data of patients with myelosuppression were worse. PA of patients with head and neck tumors are closely related to myelosuppression and low PA patients are more likely to cause myelosuppression. Monitoring PA can detect the potential risk of myelosuppression which helps to conduct nutritional intervention in time and improve prognosis.