Abstract: Objective To establish a nomogram model for predicting spontaneous bacterial peritonitis (SBP) in patients with cirrhotic ascites, and perform internal and external validation to assess its predictive value. Methods A total of 465 patients with cirrhotic ascites in the Affiliated Hospital of Xuzhou Medical University were enrolled and their clinical data were retrospectively analyzed. The patients were divided into two groups: a model group (n=368) and a validation group (n=97). According to the occurrence of SBP, patients in the model group was subdivided into two groups: a SBP group (n=172) and a non-SBP group (n=196), whereas those in the validation group was subdivided into two groups: a SBP group (n= 41) and a non-SBP group (n=56). Univariate and multivariate logistic regression analyses were performed to analyze the independent risk factors for the occurrence of SBP in the model group, and a prediction nomogram model was established. The established prediction model was internally and externally validated using the area under the curve (AUC) of receiver operating characteristic (ROC) curve, the calibration curve, and decision curve analysis (DCA) in the model and validation groups, respectively. Results According to multivariate logistic regression analysis in the model group, systemic immunoinflammatory index (SII) (OR 1.006, 95%CI 1.003-1.008, P<0.01), C-reactive protein/albumin ratio (CAR) (OR 3.968, 95%CI 1.702-9.247, P<0.01), prothrombin time (PT) (OR 1.281, 95%CI 1.282-9.247, P<0.01), mean platelet volume (MPV) (OR 1.557, 95%CI 1.245-1.947, P<0.01), and total bilirubin (TBIL) (OR 1.006, 95%CI 1.001-1.011, P<0.05) were the independent risk factors for SBP in patients with cirrhotic ascites. The AUC of the nomogram model based on SII and CAR was 0.865, with a sensitivity of 80.2%, and a specificity of 80.1%. Conclusions The nomogram model based on SII and CAR has good value of application for predicting the risk of occurrence of SBP in patients with cirrhotic ascites.