Objective To determine the factors that cause postoperative malnutrition in patients with oral cancer. Method A total of 420 patients with good preoperative nutritional status who underwent oral cancer surgery in the Department of Head and Neck Oncology at West China Hospital of Stomatology Sichuan University from August 2023 to May 2024 were selected through convenience sampling and their information was collected. Nutritional assessment was performed adopting the Nutritional Risk Screening 2002 NRS 2002 and Global Leadership Initiative on Malnutrition GLIM standards on the 7th day after the operation. Logistic regression was used to analyze the factors leading to postoperative malnutrition in patients with oral cancer. Result The prevalence of postoperative malnutrition in oral cancer patients was 50. 24%. Logistic regression analysis showed that male OR = 2. 575 95%CI = 1. 452- 4. 564 free flap transplantation OR = 2. 479 95% CI = 1. 158 - 5. 307 preoperative lymphocyte count OR= 0. 223 95%CI = 0. 139-0. 359 and preoperative total cholesterol OR = 0. 762 95%CI = 0. 596-0. 975 were independent influencing factors of postoperative malnutrition in oral cancer patients P< 0. 05 . Conclusion In the face of the high incidence of postoperative malnutrition in patients with oral cancer nutrition support teams should conduct dynamic screening and assessment of perioperative nutritional status of patients with oral cancer and provide targeted nutritional management to patients with high risk of malnutrition so as to prevent and reduce the occurrence and development of postoperative malnutrition in oral cancer patients.