Objective To investigate the cause of an outbreak of peritonitis in peritoneal dialysis patients. Methods A case-control study was conducted to explore the risk factors for the outbreak of peritoneal dialysis-related peritonitis in the renal disease center of a tertiary first-class hospital from June 1 to August 17, 2019; high risk factors were further verified by cohort study. Microbial culture of dialysis products of patients with peritonitis was performed to explore possible pathogens. Results The case-control study showed that the use of "YW" brand iodophor cap was an independent risk factor for this outbreak of peritoneal dialysis-related peritonitis, the adjusted OR was 15.40 and the 95%CI was 2.93-80.95. The cohort study confirmed that the use of "YW" brand iodophor cap was the cause of this outbreak, with an HR of 6.81 and the 95%CI of 2.61-17.77. Bacterial culture and endotoxin test results of specimens of "YW" brand iodophor cap and peritoneal dialysate were all negative, stopping the use of "YW" brand iodophor cap, incidence of peritoneal dialysis-related peritonitis decreased to the average level in the past 4 years, and it was determined that this peritoneal dialysis-related peritonitis was chemical peritonitis. Conclusion The outbreak is peritoneal dialysis-related chemical peritonitis in peritoneal dialysis patients due to the use of "YW" brand iodophor cap.