Objective  To investigate the changes in serum levels of sphingosine‑1‑phosphate receptor 1 (S1P1), soluble CD14 subtype (sCD14‑ST), and stress‑induced protein 2 (Sestrin2) in peritoneal dialysis (PD) patients with septic peritonitis (SP), and to evaluate their diagnostic value.  Methods  PD patients treated at Shenzhen Longgang Central Hospital from July 2022 to July 2025 were enrolled and divided into an SP group and a non‑SP group according to the presence of SP. Serum levels of S1P1, sCD14‑ST, and Sestrin2 were measured by ELISA. Logistic regression was used to analyze influencing factors. Receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic value. Internal validation was conducted using the Bootstrap method. Model calibration was assessed with the Hosmer‑Lemeshow test, and clinical utility was evaluated using decision curve analysis (DCA).  Results  A total of 92 patients were included, with 33 in the SP group and 59 in the non‑SP group. Among the pathogenic organisms, Gram‑negative bacteria accounted for 22 strains (62.86%) and Gram‑positive bacteria for 13 strains (37.14%). Compared with the non‑SP group, the SP group had significantly higher serum levels of C‑reactive protein (CRP), sCD14‑ST, and Sestrin2, and lower levels of albumin (Alb) and S1P1 (t = 17.840, 7.053, 7.395, 5.189, and 7.053, respectively, all  P＜0.001). Serum levels of S1P1 (OR=0.493, 95% CI: 0.318～0.765, P=0.002), sCD14‑ST (OR=2.305, 95% CI: 1.202～4.419, P=0.012), and Sestrin2 (OR=2.918, 95% CI: 1.416～6.014, P=0.004) were factors influencing the occurrence of SP in PD patients. The areas under the ROC curve (AUC) for S1P1, sCD14‑ST, Sestrin2 alone, and their combination in diagnosing SP in PD patients were 0.887～(95% CI: 0.804～0.944), 0.796 (95% CI: 0.699～0.873), 0.801 (95% CI: 0.705～0.877), and 0.948 (95% CI: 0.881～0.984), respectively. The combined diagnostic performance was superior to each individual marker (Z/P = 2.079/0.038, 2.948/0.003, and 2.893/0.004, respectively).  Conclusion  In PD patients with SP, serum S1P1 level is decreased, while sCD14‑ST and Sestrin2 levels are increased. The combination of these three markers demonstrates higher diagnostic efficacy for SP in PD patients.