Objective  To investigate the relationship between geriatric nutritional risk index (GNRI) and treatment effect of peritoneal dialysis-associated peritonitis (PDAP) in elderly patients.  Methods  A total of 147 PDAP patients treated in Qingdao Municipal Hospital from January 2020 to January 2023 were selected as the research subjects. They were divided into a cured group (102 cases) and a failed group (45 cases) based on the treatment outcome of PDAP. GNRI scores and clinical characteristics of the two groups were compared. The relationship between GNRI score and treatment outcome of PDAP patients was analyzed.  Results  There were 102 patients in the cured group and 45 patients in the failed group (including death 25 cases, withdrawal of the tubes 10 cases, and  transferred to other hospitals 10 cases) after the treatment. Compared with the cure group, GNRI score, body mass index (BMI), hemoglobin (Hb) and albumin (ALB) were significantly reduced (t=5.134, 7.517, 2.336 and 3.259 respectively; P＜0.001, ＜0.001, 0.021 and 0.001 respectively), while dialysis age was significantly increased (t=10.924, P=0.000) in the failed treatment group. Multivariate logistic regression analysis showed that lower GNRI score (OR=0.541, 95% CI: 0.335～0.872, P＜0.001), lower serum ALB (OR=0.638, 95% CI: 0.494～0.825, P＜0.001) and longer dialysis age (OR=1.674, 95% CI:1.081～2.591,P＜0.001) were the independent risk predictors for treatment failure of PDAP patients. ROC analysis showed that the area under ROC curve of GNRI score to predict treatment failure of PDAP patients was 0.735, with the sensitivity of 89.55%, the specificity of 75.43%, the Yoden index of 0.649, and the best predictive value of 90.53.   Conclusion   Decreased GNRI score is an independent risk factor for treatment failure of PDAP patients, and is highly efficient for the prediction of treatment failure in PDAP patients. Therefore, early correction of abnormal nutritional status can improve the treatment outcome of PDAP.