Objective Based on the capability opportunity motivation - behavior COM-B model this study aimed to analyze changes in dietary structure characteristics among patients with cervical cancer before and after radiotherapy and explore factors influencing their nutritional status. Method A total of 200 patients with cervical cancer admitted to the First Affiliated Hospital of Bengbu Medical University between January 2023 and December 2024 were enrolled. Changes in dietary structure before and after radiotherapy were investigated. Patients were divided into a normal nutritional status group n = 114 and an abnormal nutritional status group n = 86 based on the controlling nutritional status CONUT score. Differences in clinical data between the two groups were analyzed and factors influencing nutritional status were explored using the COM - B model. Result The Chinese Dietary Pyramid CHFP score of patients with cervical cancer was 31. 54 ± 4. 57 before radiotherapy and 22. 24 ± 2. 68 after radiotherapy indicating a significant deterioration in dietary structure post - radiotherapy. Multivariate Logistic regression analysis revealed that nutritional knowledge OR= 0. 930 95%CI = 0. 901-0. 959 self-management OR= 0. 952 95%CI = 0. 915-0. 990 payment method OR= 3. 251 95% CI = 1. 372 - 7. 704 monthly household income OR = 4. 195 95% CI = 1. 637 - 10. 746 social support OR = 0. 689 95%CI = 0. 602 - 0. 788 coping style OR = 2. 677 95% CI = 1. 112 - 6. 443 and self - efficacy OR = 0. 963 95% CI = 0. 931-0. 996 were significant influencing factors of nutritional status all P< 0. 05 . The combined indicators showed an AUC of 0. 926 for predicting nutritional status with a sensitivity of 89. 50% and specificity of 86. 80%. Conclusion The dietary structure of patients with cervical cancer is unreasonable. Clinically dietary interventions based on the COM-B model may be implemented to improve their nutritional status.