Objective To explore risk factors of unplanned reoperations in patients with malignant tumors of abdominal pelvic cavity and digestive tract based on controlled nutritional status score. Method The clinical data of patients underwent unplanned reoperation who treated in Medical Administration of the Affiliated Cancer Hospital of Shandong First Medical University from January 2020 to December 2021 were retrospectively collected and each operation was matched in a ratio of 1 ∶ 1 as a case -control study object. Univariate analysis was done by χ 2 or t test and multivariate analysis was performed by conditional logistic regression. Result The incidence of unplanned reoperation in our hospital from 2020 to 2021 was 0. 68% . The results of Univariate analysis showed that COUNT≥4 anemia and hypo-albuminemia before operation weight loss ≥2 kg in 1 month before operation operation duration ≥5 h blood loss ≥250 ml during surgery were risk factors P < 0. 05 . Conditional logistic regression multivariate analysis showed that CONUT score blood loss ≥250 ml during surgery and weight loss ≥2 kg in 1 month before operation were independent risk factors for unplanned reoperation. Conclusion Poor immunonutrition status before operation is a independent risk factor for unplanned reoperation of abdominal pelvic and gastrointestinal tract. Effective intervention on independent risk factors can reduce incidence of unplanned reoperation in future and improve prognosis.