Objective To explore the influence of preoperative nutrition risk screening on the rehabilitation of patients with colorectal cancer after radical resection and the risk factors of postoperative complications. Methods A prospective study was conducted on 110 patients with colorectal cancer who underwent radical resection in Huizhou First Hospital from July 2021 to June 2022, according to the results of preoperative nutritional risk screening, the patients were divided into the nutritional risk group (68 cases) and the non nutritional risk group (42 cases). The clinical characteristics, perioperative indicators and postoperative complications of the two groups were compared, and the patients were divided into the complication group (28 cases) and the non complication group (82 cases) according to whether there were postoperative complications. The general data of patients in the complication group and the non complication group were analyzed by single factor analysis, and the risk factors of complications in patients with colorectal cancer after radical resection were screened by multiple factor Logistic regression analysis. Results Body mass index (BMI), body fat percentage, lean tissue, serum prealbumin (PA), and peripheral blood lymphocyte (PBL) levels in the nutritional risk group were significantly lower than those in the non nutritional risk group, the total incidence of postoperative complications in the nutritional risk group was significantly higher than that in the non nutritional risk (all P<0.05); the proportion of patients with age>60 years old, combined with diabetes mellitus, American Society of Anesthesiologists (ASA) grade Ⅲ ~ Ⅳ , preoperative nutritional risk, and low differentiation of tumor in the complication group were significantly higher than those in the non complication group (all P<0.05); multiple factor Logistic regression analysis showed that age>60 years old, combined with diabetes mellitus, ASA grade Ⅲ~Ⅳ, and preoperative nutritional risk were all risk factors for complications in patients with colorectal cancer after radical resection (OR = 3.370, 3.943, 1.952, 2.273, all P<0.05). Conclusion The body composition index of colorectal cancer patients with preoperative nutritional risk significantly reduced, and the risk of postoperative complications was high, preoperative nutrition risk screening can guide the formulation of nutrition support strategies, and the clinicians should pay close attention to colorectal cancer patients with preoperative nutritional risk, age>60 years old, combined with diabetes mellitus, ASA grade Ⅲ ~ Ⅳ , which is helpful to reduce the risk of postoperative complications.