Objective To investigate the application value of geriatric nutritional risk index(GNRI)in perioperative nutritional support in elderly patients with gastrointestinal tumors.Methods A total of 121 elderly patients with gastrointestinal tumor surgery who were admitted to Shangrao People′s Hospital from February 2021 to February 2022 were selected as research objects,and they were divided into the control group(60 cases)and the experimental group(61 cases)according to random number table method.Nutritional risk screening 2002(NRS-2002)was used in the control group,and GNRI was used in the experimental group.Nutritional support plan was formulated according to the results of nutritional screening.The hospital stay,medical expenses,postoperative complications,and mortality were compared between the two groups.Receiver operating characteristic(ROC)curve analysis was used to obtain GNRI on the 3rd postoperative day,peripheral blood neutrophil/lymphocyte ratio(NLR)on the 3rd postoperative day,and GNRI combined with NLR on the 3rd postoperative day to predict the predictive value of postoperative complications in patients with gastrointestinal tumors.Results The hospital stay in the experimental group was shorter than that in the control group,and the medical expenses in the experimental group was lower than that in the control group,with statistically significant differences(P＜0.05).The incidence of postoperative complications of anastomotic leakage and fever in the experimental group were lower than those in the control group,and the differences were statistically significant(P＜0.05).There was no significant difference in mortality between the two groups(P＞0.05).Through ROC curve analysis,the area under the curve(AUC)of GNRI for predicting postoperative complications in elderly patients with gastrointestinal tumors on the 3rd day after surgery was 0.782(95%CI:0.702-0.862,P＜0.05),and the sensitivity was 0.981,specificity was 0.529,and the critical value was 97.53 points.The AUC of NLR for predicting postoperative complications in elderly patients with gastrointestinal tumors on the 3rd day after surgery was 0.921(95%CI:0.873-0.969,P＜0.05),with a sensitivity of 0.811 and a specificity of 0.926,and the critical value was 11.86.The AUC of GNRI combined with NLR for predicting postoperative complications in elderly patients with gastrointestinal tumors on the 3rd day after surgery was 0.964,the sensitivity was 0.906,and the specificity was 0.912.Conclusion GNRI can better reflect the perioperative nutritional status of elderly patients with gastrointestinal tumors.GNRI combined with NLR can predict postoperative complications on the 3rd day after surgery,which is suitable for clinical application.